Generic authorship and uncle inclusion module (#2941)

* generalized uncle processing

* add some uncle tests

* set author and do event handling

* OnePerAuthorPerHeight no longer O(n^2) and test

* bump impl_version of node

* Documentation and style fixes

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* fix #2949: index-based FindAuthor wrapper for srml-session

* use for_each_tuple

substrate/srml/support/src/lib.rs

@@ -64,6 +64,7 @@ pub use self::hashable::Hashable;
 pub use self::dispatch::{Parameter, Dispatchable, Callable, IsSubType};
 pub use self::double_map::StorageDoubleMapWithHasher;
 pub use runtime_io::{print, storage_root};
+pub use runtime_primitives::ConsensusEngineId;
 
 /// Macro for easily creating a new implementation of the `Get` trait. Use similarly to
 /// how you would declare a `const`:

substrate/srml/support/src/traits.rs

@@ -23,6 +23,7 @@ use crate::codec::{Codec, Encode, Decode};
 use crate::runtime_primitives::traits::{
 	MaybeSerializeDebug, SimpleArithmetic
 };
+use crate::runtime_primitives::ConsensusEngineId;
 
 use super::for_each_tuple;
 
@@ -102,6 +103,20 @@ impl<T> MakePayment<T> for () {
 	fn make_payment(_: &T, _: usize) -> Result<(), &'static str> { Ok(()) }
 }
 
+/// A trait for finding the author of a block header based on the `PreRuntime` digests contained
+/// within it.
+pub trait FindAuthor<Author> {
+	/// Find the author of a block based on the pre-runtime digests.
+	fn find_author<'a, I>(digests: I) -> Option<Author>
+		where I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>;
+}
+
+/// A trait for verifying the seal of a header and returning the author.
+pub trait VerifySeal<Header, Author> {
+	/// Verify a header and return the author, if any.
+	fn verify_seal(header: &Header) -> Result<Option<Author>, &'static str>;
+}
+
 /// Handler for when some currency "account" decreased in balance for
 /// some reason.
 ///