Merge pull request #1 from ChrisBeaumont/master

Tweak post prune logic, min_delta criteria
Style change to post_pruning.
Changed post_pruning to prune.
Docstrings for new helper functions.
Extend comparison test to index maps.
Update name to prune in tests.
Removed min_value, added warnings and updates for params, minor docstring changes.
Update _merge_with_parent call.
Avoid warnings if param isn't changed in prune.
Fixed warning description.
Merge pull request #111 from e-koch/master

Pruning computed dendrograms.
Memoize catalog statistics for speed

See #114
tweak input types for caching