Pool: parallel ready and runtime changes (#922)

* Revert "Revert runtime changes."

This reverts commit 01a7d1aa83c2918dd63b7dc54eb688d544cfc649.

* Parallel queue reads.

* Avoid recursion in best iterator.

substrate/core/rpc/src/author/mod.rs

@@ -127,7 +127,7 @@ impl<B, E, P> AuthorApi<ExHash<P>, BlockHash<P>, ExtrinsicFor<P>, Vec<ExtrinsicF
 	}
 
 	fn pending_extrinsics(&self) -> Result<Vec<ExtrinsicFor<P>>> {
-		Ok(self.pool.all(usize::max_value()))
+		Ok(self.pool.ready().map(|tx| tx.data.clone()).collect())
 	}
 
 	fn watch_extrinsic(&self, _metadata: Self::Metadata, subscriber: pubsub::Subscriber<Status<ExHash<P>, BlockHash<P>>>, xt: Bytes) {