Initial version of the animations module
animations.anim: Add the `delay` argument
animations.anim: Add the `infinite` argument
Define/clarify/test Progress and anim behavior with zero/negative times
animations.anim: Add the `strength` argument
Merge in easings
aminations: Add easing argument to anim()
animations: Provide a Future to let people know when an animation is done
easings.partial: Fix the result's signature
easings: Docs OCD
Add the cubic bézier easing
easings: Make a class for the easings

This changes the API a bit.
easings: Improve parametrization and names
Expose the Easing class, improve docs
easing: Autodocument parameters, auto-add graphs to Easing docs
expressions: Simplify Reduce operations with identity elements
expressions: Simplify Interpolation from Constant to Constant
Merge in 'properties'

Conflicts:
	gillcup/__init__.py
properties: Add anim() method to property values
properties: Document property animation