Offchain Workers: Example Pallet (#4989)

* Example of offchain worker pallet.

* Fix compilation issues.

* Use serde_json to parse JSON.

* Add some basic tests.

* Working on docs.

* Fix compilation

* Finish docs for signed.

* Work on unsigned send.

* Add some tests and missing docs.

* Add example of StorageValueRef

* Add weight.

* Extra \n

* Fix im-online test.

* Bump runtime.

* Fix tests.

* Apply suggestions from code review

Co-Authored-By: Joshy Orndorff <JoshOrndorff@users.noreply.github.com>
Co-Authored-By: Gavin Wood <gavin@parity.io>

* Address review comments.

Co-authored-by: Joshy Orndorff <JoshOrndorff@users.noreply.github.com>
Co-authored-by: Gavin Wood <github@gavwood.com>

substrate/frame/im-online/src/lib.rs

@@ -341,8 +341,6 @@ decl_module! {
 
 		// Runs after every block.
 		fn offchain_worker(now: T::BlockNumber) {
-			debug::RuntimeLogger::init();
-
 			// Only send messages if we are a potential validator.
 			if sp_io::offchain::is_validator() {
 				for res in Self::send_heartbeats(now).into_iter().flatten() {