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

* BlockId in client interface

* Sync fixes and tests

* Updated to latest primitives

* Updated dependencies

* Updated for new (old) primitives

* Network as workspace member

* substrate-network

* Removed obsolete file

* begin_transaction on hash