* move validity module to disputes module

* prepare a section on approvals

* extract approval/assignments text to an overview section

* Apply suggestions from code review

Spelling

Co-authored-by: Fedor Sakharov <fedor.sakharov@gmail.com>

* Initial guide modifications for approvals

* Split approval assignments keys and approval votes keys

This should avoid the political problems with validator operators
wnting everything to be a remote signer.

* Update roadmap/implementers-guide/src/runtime/validity.md

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

* Update roadmap/implementers-guide/src/node/validity/assignments.md

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

* Update roadmap/implementers-guide/src/node/validity/assignments.md

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

* Update roadmap/implementers-guide/src/node/validity/assignments.md

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

* Update roadmap/implementers-guide/src/node/validity/assignments.md

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

* Update roadmap/implementers-guide/src/node/validity/assignments.md

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

* Update roadmap/implementers-guide/src/node/validity/assignments.md

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

* Update roadmap/implementers-guide/src/node/validity/assignments.md

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

* Update roadmap/implementers-guide/src/node/validity/approvals.md

Co-authored-by: hndnklnc <handankilinc1@gmail.com>

* Update roadmap/implementers-guide/src/node/validity/approvals.md

Co-authored-by: hndnklnc <handankilinc1@gmail.com>

* Update roadmap/implementers-guide/src/runtime/validity.md

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

* Not sure where these go..

* Update roadmap/implementers-guide/src/node/validity/approvals.md

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

* Local clock leniency

* Explain HSM blabla

* double word

* Clarify okasing things on-chain

* Assignments integration with relative time

* minor tweaks

* Clarify structure and work savings

* Use included more

* Cleanup and paramaters

See https://github.com/w3f/research-internal/issues/515



* More on GRANDPA

* Explain relay equivocation relevance

* Address postponement and on-chain verification somewhat

* small bit more explination

* just use ed25519 here: could -> should

* spelling

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>
Co-authored-by: hndnklnc <handankilinc1@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

* adjust to relative links

* additional adjustment to relative link

* link directly to file

* link directly to file

* 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