Replace Coyoneda.apply with a fully-powered version.

* The old Coyoneda.apply is now called 'lift'.

* Both *Coyoneda have 'unlift' aliases for 'run'.

* More construction facilities for Coyoneda copied from
  ContravariantCoyoneda.

* Coyoneda is now sealed.

* Coyoneda only has abstract values now, no abstract methods, and
  there is only one (private) concrete class.