* scheduler: handle re-scheduling around finalization correctly

* also make sure parathreads get cleaned

* run scheduling in finalization

* Remove stray println!

* Update the schedule call site in inclusion inherent

* Clarify subtlety around SessionStartBlock

* Remove double semi-colon

* reschedule prior to `availability_cores` and in on-initialize

* improve docs

* fix line

* more doc reformat

* remove unneeded call

* avoid unnecessary scheduling on initialize

* split `clear` and `schedule

* Update runtime/parachains/src/scheduler.rs

Co-authored-by: Sergei Shulepov <sergei@parity.io>

Co-authored-by: Sergei Shulepov <sergei@parity.io>

* Cont.: Implement the state root obtaining during inclusion

During inclusion now we obtain the storage root by passing it through
the inclusion_inherent.

* Fix tests

* Bump rococo spec version

* Reorder the parent header into the end

of the inclusion inherent.

When the parent header is in the beginning, it shifts the other two
fields, so that a previous version won't be able to decode that. If
we put the parent header in the end, the other two fields will stay
at their positions, thus make it possible to decode with the previous
version.

That allows us to perform upgrade of rococo runtime without needing of
simultanuous upgrade of nodes and runtime, or restart of the network.

* Squash a stray tab

* Guide: Split router module in guide.

Now we have: DMP, UMP and Router module.

* Add a glossary entry for what used to be called Router

* Extract DMP

* Extract UMP

* Extract HRMP

* Switch over to new modules

* Router: goodbye sweet prince

* Link to messaging overview for details.

* Update missed rococo and test runtimes.

* Commit destroyed by rebase changes

* Don't deprecate Router but rather make it a meta-project

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Fix typos suggestion

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Fix repetition in the impl guide

* Clarify that processed_downward_messages has the u32 type

* Remove the router subdir.

* Deabbreviate DMP,UMP,HRMP

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* UMP: Update the impl guide

* UMP: Incorporate XCM related changes into the guide

* UMP: Data structures and configuration

* UMP: Initial plumbing

* UMP: Data layout

* UMP: Acceptance criteria & enactment

* UMP: Fix dispatcher bug and add the test for it

* UMP: Constrain the maximum size of an UMP message

This commit addresses the UMP part of https://github.com/paritytech/polkadot/issues/1869



* Fix failing test due to misconfiguration

* Make the type of RelayDispatchQueueSize be more apparent in the guide

* Revert renaming `max_upward_queue_capacity` to `max_upward_queue_count`

* convert spaces to tabs

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Update runtime/parachains/src/router/ump.rs

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Guide: Reindent the router module with 4 spaces

The guide used to use 2 spaces for indentation. The problem with that is `mdbook` doesn't recognize them as a proper indentation and thus doesn't render indent properly.

A couple of things are not indented here because they will be changed in the following commits

* Guide: a bunch of fixes

* Take 2 at the upward messages

* Trying to restore stuff from unsuccesful rebase

* Fix whitespace

* Clean up

* Change rustdoc to comment

* Pivot to a less stricter, w.r.t. to acceptance, model

* Rename `max_upward_message_num_per_candidate`

* Update docs for DownwardMessage

* Apply suggestions from code review

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* Rephrase "Dispatchable objects ready to ..."

* Finish the sentence

* Add a note about imprecision of the current weight formula

* Elaborate on potential use-cases for the upward message kinds.

* s/later/below

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* rename implementor's guide to implementer's guide

* fix typos in more places

* Add mdbook-linkcheck

* Convert todo to not a link

* Fix external glossary link

* Fix various broken links

* Mass replace: s/.html/.md/

* My sloppy attempt to add a gitlab CI check

* add availability bitfield types to primitives

* begin inclusion module

* use GitHub issue link for limitation

* fix some compiler errors

* integrate validators into initializer

* add generic signing context

* make signing-context more generic

* fix issues with inclusion module

* add TODO

* guide: add validators and session index to inclusion

* guide: add session index to change notification

* implement session change logic

* add BackedCandidate type

* guide: refine inclusion pipeline

* guide: rename group_on to group_validators

* guide: add check about collator for parathread

* guide: add last_code_upgrade to paras and use in inclusion

* implement Paras::last_code_upgrade

* implement most checks in process_candidates

* make candidate receipt structs more generic

* make BackedCandidate struct more generic

* use hash param, not block number

* check that candidate is in context of the parent block

* include inclusion module in initializer

* implement enact-candidate

* check that only occupied cores have bits set

* finish implementing bitfield processing

* restructure consistency checks on candidates

* make some more primitives generic

* signature checking logic for backed candidates

* finish implementing process_candidates

* implement collect_pending

* add some trait implementations to primitives

* implement InclusionInherent and squash warnings

* test bitfield signing checks

* rename parachain head to para_head

* fix note_new_head bug in paras

* test bitfield enactment in inclusion

* helpers for candidate checks

* add test for most candidate checks

* add test for backing setting storage

* test session change logic

* remove extraneous type parameter

* remove some allow(unused)s

* extract threshold computation to const fn

* remove some more allow(unused)s

* improve doc

* add debug assertion

* fix primitive test compilation

* tag unanimous variant as unused

* types chapter & candidate types

* Factor out some message types

* backing and availability types.

* spacing

* finish thought

* info on signed payloads

* update links

* explicit wrapper types

* add remaining message types

* add runtime API subsystem

* adjust language

* tweak candidate validation message

* find homes for some misfit types

* embed abridged within full candidate receipt

* Update roadmap/implementors-guide/src/SUMMARY.md

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* Update roadmap/implementors-guide/src/SUMMARY.md

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* adjust text on candidate selection message to match

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* adjust to relative links

* additional adjustment to relative link

* link directly to file

* link directly to file

* scheduler module skeleton

* update scheduler skeleton to match latest version of guide

* better session change notification

* add mock randomness and fix test compilation

* shuffle validators into groups

* finish implementing session change logic for scheduler

* tweak core assignment type to track retries of parathread

* reframe queued parathread core as offset

* implement initialzation and finalization routines

* implement parathread claim queuing

* implement core_para

* implement the group_validators routine and fix errors

* add a reason for freeing cores

* implement `schedule` function

* add some docs to the scheduled function

* implement `occupied` helper

* implement availability predicate

* fix some warnings

* integrate scheduler into initializer

* integrate scheduler into mock module

* avoid conflict with Substrate's scheduler storage

* add parathreads index to paras module

* implement parathreads map in paras module

* add is_parathread to paras

* test adding parathread claim

* test that you cannot add claims when no parathread cores exist

* check session change parathread queue pruning

* test validator shuffling

* add allow_unused to scheduler items

* add test for scheduling

* add some more tests for scheduling logic

* test core rotation

* check parathread claim pruning after retries

* add bound notes

* Apply suggestions from code review

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* more suggestions from review

* test availability predicate, add box to please compiler

* add changes to guide

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* move old implementers' guide, add skeleton of new

* Split the old implementers' guide into the new one's sections

This is mostly a straightforward copying operation, moving the
appropriate sections from the old guide to the new. However, there
are certain differences between the old text and the new:

- removed horizontal rules between the sections
- promoted headers appropriately within each section
- deleted certain sections which were in the old guide's ToC but
  which were not actually present in the old guide.
- added Peer Set Manager to the new ToC

* remove description headers

It is redundant and unnecessary. Descriptions fall directly under the
top-level header for any given section.

* add stub description of the backing module

* add stub description for the availability module

* add stub description for collators

* add stub description for validity

* add stub description for utility

* highlight TODO and REVIEW comments

* add guide readme describing how to use mdbook

* fix markdownlint lints

* re-title parachains overview

* internal linking for types

* module and subsystem internal links

* .gitignore should have a trailing newline

* node does not have modules, just subsystems