v2.1.1

Add some new time units, and small fixes to some existing units.

v2.1.0

This version adds dual compatibility for Python 2 and 3. At this stage, Python 3 runs the benchmarks in test.py a little slower than Python 2.

v2.0.0

Bump version to 2.0.0; and update documentation accordingly.

v1.9.1

Bump version number to 1.9.1.