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/node/runtime/src/lib.rs

@@ -232,7 +232,7 @@ pub type Executive = executive::Executive<Runtime, Block, Balances, Balances, Al
 pub mod api {
 	impl_stubs!(
 		version => |()| super::VERSION,
-		json_metadata => |()| super::Runtime::json_metadata(),
+		metadata => |()| super::Runtime::metadata(),
 		authorities => |()| super::Consensus::authorities(),
 		initialise_block => |header| super::Executive::initialise_block(&header),
 		apply_extrinsic => |extrinsic| super::Executive::apply_extrinsic(extrinsic),

substrate/node/runtime/wasm/Cargo.lock

@@ -879,6 +879,9 @@ name = "substrate-metadata"
 version = "0.1.0"
 dependencies = [
  "parity-codec 1.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "parity-codec-derive 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
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