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/sr-primitives/src/lib.rs

@@ -64,11 +64,23 @@ pub type Justification = Vec<u8>;
 
 use traits::{Verify, Lazy};
 
-/// A String that is a `&'static str` on `no_std` and a `String` on `std`.
-#[cfg(not(feature = "std"))]
-pub type RuntimeString = &'static str;
+/// A String that is a `&'static str` on `no_std` and a `Cow<'static, str>` on `std`.
 #[cfg(feature = "std")]
 pub type RuntimeString = ::std::borrow::Cow<'static, str>;
+#[cfg(not(feature = "std"))]
+pub type RuntimeString = &'static str;
+
+/// Create a const [RuntimeString].
+#[cfg(feature = "std")]
+#[macro_export]
+macro_rules! create_runtime_str {
+	( $y:expr ) => {{ ::std::borrow::Cow::Borrowed($y) }}
+}
+#[cfg(not(feature = "std"))]
+#[macro_export]
+macro_rules! create_runtime_str {
+	( $y:expr ) => {{ $y }}
+}
 
 #[cfg(feature = "std")]
 pub use serde::{Serialize, de::DeserializeOwned};