Allow parachains to send messages (#274)

* Slots module

* Integrate slots

* More drafting

* Minor updates

* Update parachains to use trati

* More build fixes

* Full code now compiles

* Add renew bid function

* Implement calculate_winner

* Warning remove

* Update gitignore

* Test framework

* Tests

* Further testing

* More tests, new parameterisation.

* Fix and new test

* Thread-safe tests

* Test off-boarding and a fix.

* Test onboarding

* Allow late onboarding.

* Another test and fix

* Avoid println in nostd

* Compact representation of paraids

* Introduce documentation.

* Introduce events.

* Additional test and fix

* Additional test

* Tidy up line lengths.

* Remove printlns

* Use later substrate utils.

* Allow parachains to send messages.

* Fix build/test

* Make slots work with latest substrate

* Update runtime/src/slot_range.rs

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

* Update runtime/src/slots.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update runtime/src/slots.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Polish logic

* Rewind to earlier substrate master

* Remove dead code.

* Fix build

* Update substrate ref to master

* Update to new inherent digests API

* address grumbles

* fix

* Fix a warning.

* Reworded a comment.

* Check that receipt matches expectations

* Add test for final checks

* Split out queuing logic.

* Test final piece of queuing logic

* Fix up docs.

* More docs fixes

polkadot/collator/src/lib.rs

@@ -152,10 +152,10 @@ pub fn collate<'a, R, P>(
 			collator: key.public(),
 			signature,
 			head_data,
-			balance_uploads: Vec::new(),
 			egress_queue_roots,
 			fees: 0,
 			block_data_hash,
+			upward_messages: Vec::new(),
 		};
 
 		Ok(parachain::Collation {