Functional reactive programming library

#15Relax contexts for AMP

A number of contexts seem oddly strong now that Applicative is a superclass of Monad. Notably, the Functor instance for Wire only needs Functor m, and I believe the Applicative instance only needs Applicative m. This spreads to things like timeF. Of course, you might want to leave it alone in case the instance definitions need to change later to use that power.