Setuptools-scm

- fix issue 128: return None when a scm specific parse fails in a
worktree to ease parse reuse

- fix issue 126: the local part of any tags is discarded when
guessing new versions
- minor performance optimization by doing fewer git calls in the usual
cases

- more sophisticated ignoring of mercurial tag commits when
considering distance in commits (thanks Petre Mierlutiu)
- fix issue 114: stop trying to be smart for the sdist and ensure it's
always correctly using itself
- update trove classifiers
- fix issue 84: document using the installed package metadata for
sphinx
- fix issue 81: fail more gracious when git/hg are missing
- address issue 93: provide an experimental api to customize
behaviour on shallow git repos a custom parse function may pick pre
parse actions to do when using git

- fix 109: when detecting a dirty git workdir

don't consider untracked file (this was a regression due to 86 in v1.13.1)
- consider the distance 0 when the git node is unknown (happens when you haven't committed anything)

- publish bdist_egg for python 2.6, 2.7 and 3.3-3.5
- fix issue 107 - dont use node if it is None

- fix issue 86 - detect dirty git workdir without tags