First step for generating host externals out of the function definition in sr-io (#3567)

* Adds new wrapper traits for wasm executor

* Add new crate `substrate-wasm-interface`

Thew new crate holds types and traits for the communicating between the
wasm runtime and the host.

* Rewrite externals with new macro etc

* Fix vec initialization

* Make executor tests working

* Remove unused code + warnings

* Introduce `Pointer` and `WordSize` for working with wasm

* Fix tests and compilation

* Fix compilation

* Apply suggestions from code review

Co-Authored-By: Sergei Pepyakin <sergei@parity.io>

* Review feedback

* Remove unused conversions

* Make each host function its own struct

`HostFunctions` now just returns these function structs. Each function
can be executed by using one of the function structs. The inherent host
functions are now moved to the "normal" host functions.

* Remove byteorder

* Add floating point types

* Make pointer interface more safe

* Add type alias for wasm-interface Result

* More review comments

substrate/core/sr-io/src/lib.rs

@@ -279,7 +279,7 @@ export_api! {
 		/// Submit transaction to the pool.
 		///
 		/// The transaction will end up in the pool.
-		fn submit_transaction<T: codec::Encode>(data: &T) -> Result<(), ()>;
+		fn submit_transaction(data: Vec<u8>) -> Result<(), ()>;
 
 		/// Returns information about the local node's network state.
 		fn network_state() -> Result<OpaqueNetworkState, ()>;