* 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