Make runtime api generate version and identifier information (#1226)

* Make `decl_runtime_apis!` implement `RuntimeApiInfo` for all runtime
apis

* Make the runtime side generate the info constants as well

* Make `RuntimeApiInfo` implementation use the correct generics

* Adds a test for the runtime api info stuff

* Remove duplicated code by using block from `test-client`

* Adds `compile_fail` tests for `api_version`

* Adds documentation for `api_version`

* Make `impl_runtime_apis!` generate `RUNTIME_API_VERSIONS`

* Update documentation and tests for `RUNTIME_API_VERSIONS`

* Implement `has_api` by using the `RuntimeApiInfo`

* Make `impl_runtime_apis` check that trait identifiers are unique

* Prefix all runtime api function with the corresponding trait

So `execute_block` will be called `Core_execute_block`.
This makes it possible to have traits implement a function with the
same name.

* Rebase master

* Update after master rebase

substrate/core/client/src/light/call_executor.rs

@@ -166,7 +166,7 @@ mod tests {
 			.unwrap().storage_root(::std::iter::empty()).0;
 
 		// 'fetch' execution proof from remote node
-		let remote_execution_proof = remote_client.execution_proof(&remote_block_id, "authorities", &[]).unwrap().1;
+		let remote_execution_proof = remote_client.execution_proof(&remote_block_id, "Core_authorities", &[]).unwrap().1;
 
 		// check remote execution proof locally
 		let local_executor = test_client::LocalExecutor::new();
@@ -179,7 +179,7 @@ mod tests {
 				extrinsics_root: Default::default(),
 				digest: Default::default(),
 			},
-			method: "authorities".into(),
+			method: "Core_authorities".into(),
 			call_data: vec![],
 			retry_count: None,
 		}, remote_execution_proof).unwrap();