Deprecate ANOSIM, PERMANOVA, and CategoricalStatsResults

Will be replaced with procedural anosim and permanova, and pandas.Series to store results.
Deprecate skbio.stats.p_value_to_str
Add procedural implementations of anosim and permanova

Still need to add tests for private functions in _base.py, update docs and doctests.
Add tests for private categorical stats helper functions
Add tests that relabeled groups produce the same results in anosim and permanova
add documentation to anosim and permanova
update pwmantel to not use p_value_to_str

also finish updating the rest of anosim's doctests
update changelog
fix test and doc failures
Merge branch 'master' into issue-754-no-really

Conflicts:
	CHANGELOG.md
Results now store general "test statistic" field

Added "test statistic name" field to describe the type of test statistic (previously stored in the field name). Thanks for the suggestion @gregcaporaso!
data frame -> DataFrame
_run_stat_method -> _run_monte_carlo_stats
Merge pull request #759 from jairideout/issue-754-no-really

Add procedural versions of ANOSIM and PERMANOVA