added pruning functions. Refactor code to use them
Backport np.unravel_multi_index for numpy <= 1.5. Update docs
Merge pull request #78 from ChrisBeaumont/prune_functions

Collection of pruning functions
Added six.py
Use six.py instead of 2to3 - code base should now be fully Python 2.x and 3.x-compatible by default.
Merge pull request #79 from astrofrog/use-six

Use six.py instead of 2to3