Replace JSON metadata with custom metadata structures (#766)

* Move module metadata from json string to custom metadata

* Revisit the metadata structures

1. Move the structures into the metadata crate.
2. Switch to using Cow/MaybeOwnedArray to support Encode/Decode

* Adapt to new metadata structures

* Convert event json metadata to new metadata structures

* Convert storage json metadata to new metadata structures

* Convert runtime metadata from json to new metadata structs

* Implements new metadata structures in client and runtime

* Fixes errors on `no_std`

* Fixes errors after rebasing master

* Do not use `Cow` anymore in metadata

Also replace `String` with our own type definition `StringBuf`.
This fixes compilation on `no_std`.

* Wrap `RuntimeMetadata` in `RuntimeMetadataVersioned` to support versioning

* Move metadata into `srml` and make core unaware of the implementation

substrate/core/test-runtime/src/lib.rs

@@ -133,21 +133,10 @@ pub fn run_tests(mut input: &[u8]) -> Vec<u8> {
 	[stxs.len() as u8].encode()
 }
 
-fn test_event_json() -> &'static str {
-	"hallo"
-}
-
 pub mod api {
 	use system;
 	impl_stubs!(
 		version => |()| super::version(),
-		json_metadata => |()| {
-			let mut vec = ::runtime_support::metadata::Vec::new();
-			vec.push(::runtime_support::metadata::JsonMetadata::Events {
-				name: "Test", events: &[ ("event", super::test_event_json) ]
-			});
-			vec
-		},
 		authorities => |()| system::authorities(),
 		initialise_block => |header| system::initialise_block(header),
 		execute_block => |block| system::execute_block(block),