Make runtime api calls native when possible (#1302)

* Add simple benchmark for the runtime api

* Make the executor support native calls

* Some documentation

* Hide behind `feature = "std"`

* Rework the native calls

* Make all tests compile again

* Make every parameter using the Block serialized/deserialized in the native call

* Forward `UnwindSafe` requirement

* Remove debug stuff

* Add some documentation

* Fixes warnings

* Fixes errors after master rebase

* Fixes compilation after master rebase

* Fixes compilation after rebase

substrate/core/consensus/aura/src/lib.rs

@@ -492,12 +492,12 @@ impl<B: Block, C, E, MakeInherent, Inherent> Verifier<B> for AuraVerifier<C, E,
 				// actually matches the slot set in the seal.
 				if let Some(inner_body) = body.take() {
 					let inherent = (self.make_inherent)(timestamp_now, slot_num);
-					let block = Block::new(pre_header.clone(), inner_body);
+					let block: B = Block::new(pre_header.clone(), inner_body);
 
 					let inherent_res = self.client.runtime_api().check_inherents(
 						&BlockId::Hash(parent_hash),
-						&block,
-						&inherent,
+						block.clone(),
+						inherent,
 					).map_err(|e| format!("{:?}", e))?;
 
 					match inherent_res {