Initial: Offchain Workers (#1942)

* Refactor state-machine stuff.

* Fix tests.

* WiP

* WiP2

* Service support for offchain workers.

* Service support for offchain workers.

* Testing offchain worker.

* Initial version working.

* Pass side effects in call.

* Pass OffchainExt in context.

* Submit extrinsics to the pool.

* Support inherents.

* Insert to inherents pool.

* Inserting to the pool asynchronously.

* Add test to offchain worker.

* Implement convenience syntax for modules.

* Dispatching offchain worker through executive.

* Fix offchain test.

* Remove offchain worker from timestamp.

* Update Cargo.lock.

* Address review comments.

* Use latest patch version for futures.

* Add CLI parameter for offchain worker.

* Fix compilation.

* Fix test.

* Fix extrinsics format for tests.

* Fix RPC test.

* Bump spec version.

* Fix executive.

* Fix support macro.

* Address grumbles.

* Bump runtime

substrate/srml/example/src/lib.rs

@@ -214,6 +214,15 @@ decl_module! {
 			// We just kill our dummy storage item.
 			<Dummy<T>>::kill();
 		}
+
+		// A runtime code run after every block and have access to extended set of APIs.
+		//
+		// For instance you can generate extrinsics for the upcoming produced block.
+		fn offchain_worker(_n: T::BlockNumber) {
+			// We don't do anything here.
+			// but we could dispatch extrinsic (transaction/inherent) using
+			// runtime_io::submit_extrinsic
+		}
 	}
 }