Introduce treasury and document (#646)

* Introduce treasury and document

* Revert bad changes

* More reversions

* Add example crate

- Remove HasPublicAux
- Rename Concrete -> Runtime

* Actually commit stuff

* Changes

* Propagate block number in finalise.

* Fix and build example

* Fixes.

* Fix compilation for treasury.

* Fix the treasury test

* Tests

* Fix.

* Fix tests

* Fix a few grumbles

* Fixes

* Fix grumbles