RLS: Version 0.2.1
Merge pull request #120 from danielballan/rls-0.2.1

RLS: Version 0.2.1
DOC/BLD: Fix setup.py for ReadTheDocs.
Merge pull request #121 from danielballan/fix-readthedocs

Fix readthedocs
REF: Support Python 3 using six.
BLD: Use skimage for all builds instead of PIL.