Rewrite impl_runtime_apis! and decl_runtime_apis! as proc-macro (#1174)

* Rewrites `impl_runtime_apis!` macro as `proc-macro`

* Adds some documentation

* Require the `impl_runtime_apis` to use a path for accessing the trait

* Make the runtime implement `GetNodeBlockType`

* Moves first chunk of runtime api code into the `impl_runtime_apis` macro

This also renames `ClientWithApi` into `RuntimeApi`.

* Make `impl_runtime_apis` use `runtime` api version automatically

* `decl_runtime_apis` automatically adds `Block: BlockT` as generic parameter

* Remove function generic arguments in block builder api

* Remove some unnused stuff from the `decl_runtime_apis` macro

* Make `InherentData` working again

* Make `impl_runtime_apis!` implement the `RuntimeApi` side as well

* Make it compile again after rebasing with master

* Split `sr-api-macros` into multiple files

* Reimplement `decl_runtime_apis!` as proc_macro

* Use `decl_runtime_apis!` for `Core` as well and improve error reporting

* Adds documentation for `decl_runtime_apis!` and `impl_runtime_apis!`

* Move some code

* Adds compile fail tests

* Adds a test and fixes some bugs

* Make `impl_runtime_apis!` support `_` as parameter name

* Fixes build errors with wasm

* Wasm rebuild after master rebase

* Apply suggestions from code review

Co-Authored-By: bkchr <bkchr@users.noreply.github.com>

* Addresses some grumbles

* Adds test to ensure that method signatures need to match

* New wasm files

substrate/core/consensus/aura/src/lib.rs

@@ -440,7 +440,7 @@ mod tests {
 
 	type Error = client::error::Error;
 
-	type TestClient = client::Client<test_client::Backend, test_client::Executor, TestBlock, test_client::runtime::ClientWithApi>;
+	type TestClient = client::Client<test_client::Backend, test_client::Executor, TestBlock, test_client::runtime::RuntimeApi>;
 
 	struct DummyFactory(Arc<TestClient>);
 	struct DummyProposer(u64, Arc<TestClient>);