Additional runtime tests for the test-runtime (#69)

* Remove rustc dependency from ed25519 and refactor a little.

* Runtime support provides more extensive test-key functionality.

* Additional APIs for ed25519 stuff.

* Extensive test for test-runtime.

* Fixes for the new test key API.

* Additional convenience for tests

* Take advantage of more convenient API.

* Redo formating.

* Remove old test identities.

* Remove boilerplate, add test.

* Refactor out unneeded code.

* Clean up algo for determining authorities.

* Remove unneeded API.

* Make `to_*` consume

* Only export keyring when testing

* Fix build & warning

* Extract Keyring into separate library.

* Add tests for Keyring and a trait-based API.

* Address grumbles.