Abstracting Active over time.
Removing need for Num in backwards.
Time should not be in the VectorSpace, AddititiveGroup or InnerSpace.

The Duration should be used instead.
Adding VectorSpace (Diff t) to Clock constraints. Removing Num.
Removing VectorSpace (Diff t) which is implied by Clock.
Adding constrains to Clock.
ui does not need Num if we use toTime.
Split into Two classes, Clock and Waiting. Lets stretchTo work.
Adding Deadline concept, for decisions about deadlines.
Adding Clock constraint to the Deadline class.
Adding transitionDeadline, which provides a switcher.
Fixing |>> and movie to use the new deadline function.
Fixing 2 bugs in |>>.
Fixing discrete's type.
Fixing simulate to use toTime/fromTime. Simplifies type.
Fixing the import list
We never actually used Boolean.
Exporting Era, mkEra
Fixing stretch to take a Rational (again), and fixing stretchTo.
Tests now compile and run correctly.