Make Clock.time into an expression
expressions: Clarify Reduce docs
expressions: Use Numpy-style rich comparisons
Merge in 'clocks'
expressions: Turn Elementwise into the more general Map
Merge in 'animations'
expressions: Make _Compare internal
expressions: Switch the order of Reduce operands

This conforms to what the built-in reduce() does

Oh, and also make Compare internal

Conflicts:
	gillcup/expressions.py
expressions: Add a ** b
Merge in 'expressions'