Merge branch 'issue564' of https://github.com/ebolyen/scikit-bio into issue-564
Merge branch 'master' into issue-564

Conflicts:
	skbio/alignment/_alignment.py
	skbio/tree/_tree.py
First working version of dm_to_DissimilarityMatrix
Refactor dm parser to support Dissimilarity/DistanceMatrix classes
Remove redundant DistanceMatrix tests
Refactor test code, much shorter/cleaner now
Make naming consistent in tests
Move docstring to module level

Docstring still needs to be updated.
Port dm writer code

Still needs unit tests.
Add dm writer tests
Port rountrip read/write test for dm format
Move writer code to keep ordering consistent with public functions
Add initial implementation of OrdinationResults.plot

Currently only supports plotting numeric metadata, and there are a large number of todos scattered throughout the code.
Update plot method to return figure
Add several input error checks to plot method
Add cmap option
Add support for plotting categorical data

Code still needs cleanup and support for a legend.
Add legend support for categorical data
Move categorical legend plotting code to private method
Refactored rest of plotting code into private methods

Also renamed several variables for clarity.