* reshuffle consensus libraries

* polkadot-useful type definitions for statement table

* begin BftService

* primary selection logic

* bft service implementation without I/O

* extract out `BlockImport` trait

* allow bft primitives to compile on wasm

* Block builder (substrate)

* take polkadot-consensus down to the core.

* test for preemption

* fix test build

* Fix wasm build

* Bulid on any block

* Test for block builder.

* Block import tests for client.

* Tidy ups

* clean up block builder instantiation

* justification verification logic

* JustifiedHeader and import

* Propert block generation for tests

* network and tablerouter trait

* use statement import to drive creation of further statements

* Fixed rpc tests

* custom error type for consensus

* create proposer

* asynchronous proposal evaluation

* inherent transactions in polkadot runtime

* fix tests to match real polkadot block constraints

* implicitly generate inherent functions

* add inherent transaction functionality to block body

* block builder logic for polkadot

* some tests for the polkadot API

* reshuffle consensus libraries

* polkadot-useful type definitions for statement table

* begin BftService

* primary selection logic

* bft service implementation without I/O

* extract out `BlockImport` trait

* allow bft primitives to compile on wasm

* Block builder (substrate)

* take polkadot-consensus down to the core.

* test for preemption

* fix test build

* Fix wasm build

* Bulid on any block

* Test for block builder.

* Block import tests for client.

* Tidy ups

* clean up block builder instantiation

* justification verification logic

* JustifiedHeader and import

* Propert block generation for tests

* Fixed rpc tests

* reshuffle consensus libraries

* polkadot-useful type definitions for statement table

* begin BftService

* primary selection logic

* bft service implementation without I/O

* extract out `BlockImport` trait

* allow bft primitives to compile on wasm

* take polkadot-consensus down to the core.

* test for preemption

* fix test build

* Introduce simple blockchain runtime for substrate tests.

* Remove bad files.

* Add needed wasm binaries.

* Refactoring.

- Repot files in test-runtime.
- Rename troublesome `Joiner::join` to `Joiner::and`.
- Rework `Slicable` to dedup code.

* More fixes and refactoring

* Rebuild substrate test wasm.

* Fix merge errors.

* Rename the disasterously named `to_vec` to `encode`.

Also rename `as_slice_then` to `with_encoded`.

* Tests for toy runtime.

* Fix doc nit

Re-introduce zero copy codec and add minimal polkadot client API which uses linked native runtime (#65)

* client-api type and move duty roster types to primitives

* tuple implementation for slicable

* mild cleanup of deserialization code

* stubs which handle encoding and decoding themselves

* fancier impl_stubs macro

* zero-copy slicable API

* minimal polkadot-client API

* fix WASM API generation

* move native environment stuff to substrate executor

* fix warnings and grumbles