Update versioneer, and fix a bug in which _version.py was not getting…

… updated during "python setup.py sdist"

(essentially, setup.py needs to get the sdist command from versioneer and not directly from distutils)

Merge pull request python-quantities#131 from apdavison/doc-update

Updates to the documentation

reverts 46c2efd, closes issue python-quantities#100

fixes a unit test, use q.nansum method, not np.nansum func

version 0.10.1