Partial support for variable-sized bins in MantelCorrelogram class.
Merge branch 'master' into mantel_correlogram_bins
Added MantelCorrelogram._find_row_col_indices(), which is necessary for variable-sized bins.
Added variable-size bin support to MantelCorrelogram._find_distance_classes().
Added --variable_size_distance_classes option to compare_distance_matrices.py script.
Fixed a couple of border-case bugs and added tests for them.
Added notes to changelog; reverted a few comments I didn't mean to add.
The coverage_category states are returned instead of their number.
Updated tests to work with new function signature.
Added optional splitter_category parameter.

Partial support for (optional) splitting of mapping file prior to filtering.
Added some preliminary error handling unit tests and pulled the "meaty" code
into a "private" function ```__filter_sample_ids_from_category_state_coverage()```.
Finished implementation of splitter_category.

Still need to add more unit tests.
Added unit test for splitter_category.

Also cleaned up some duplicate code in the unit tests and added docstrings to
new helper function.
Updated ChangeLog.
Updated splitter_category docstring.

Improves clarity.
Merge pull request #627 from jrrideout/mantel_correlogram_bins

Added support for variable-size distance classes in Mantel correlogram.
Merge branch 'master' into timeseries_filtering

Conflicts:
	ChangeLog.md
Update doc/scripts/beta_diversity_metrics.rst

this file was missing the binary_out_gain option that is present in Qiime. I am not sure what the description should be so I copied the Qiime Feb 2011 changelog where this was intriduced for the first time
use BIOM Table API instead of per-element lookups
improved varible name
added contribution