Move inherent implementation into the modules (#924)

* Adds new `ProvideInherent` trait

Also implements the new trait for `srml/consensus` and `srml/timestamp`.

* Adds `impl_outer_inherent!` macro

* Reexport macros from `alloc`

* Introduce `RuntimeString` and fix `ProvideInherent` on `no_std`

* Replace `VersionString` with `RuntimeString`

* Improvements for `impl_outer_inherent!`

* Make `construct_runtime!` support `impl_outer_inherent!`

* Fixes after rebase

* Whitespace

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

@@ -22,8 +22,6 @@ extern crate sr_std as rstd;
 extern crate sr_primitives as primitives;
 #[doc(hidden)]
 pub extern crate parity_codec as codec;
-#[macro_use]
-extern crate parity_codec_derive;
 extern crate sr_version as runtime_version;
 
 #[doc(hidden)]
@@ -429,17 +427,6 @@ macro_rules! decl_apis {
 	};
 }
 
-//TODO: Move into runtime!
-#[derive(Encode)]
-#[cfg_attr(feature = "std", derive(Debug, Decode))]
-pub enum BlockBuilderError {
-	#[cfg(not(feature = "std"))]
-	Generic(&'static str),
-	#[cfg(feature = "std")]
-	Generic(String),
-	TimestampInFuture(u64),
-}
-
 decl_apis! {
 	/// The `Core` api trait that is mandantory for each runtime.
 	pub trait Core<Block: BlockT, AuthorityId> {
@@ -482,7 +469,7 @@ decl_apis! {
 		/// Generate inherent extrinsics.
 		fn inherent_extrinsics<InherentExtrinsic, UncheckedExtrinsic>(inherent: InherentExtrinsic) -> Vec<UncheckedExtrinsic>;
 		/// Check that the inherents are valid.
-		fn check_inherents<InherentData>(block: Block, data: InherentData) -> Result<(), BlockBuilderError>;
+		fn check_inherents<InherentData, Error>(block: Block, data: InherentData) -> Result<(), Error>;
 		/// Generate a random seed.
 		fn random_seed() -> <Block as BlockT>::Hash;
 	}