Setuptools-scm

- always run tag_to_version so in order to handle prefixes on old
setuptools (thanks to Brian May)
- drop support for python 3.2
- extend the error message on missing scm metadata (thanks Markus
Unterwaditzer)
- fix bug when using callable version_scheme (thanks Esben Haabendal)

- fix issue 73 - in hg pre commit merge, consider parent1 instead of
failing

- add support for overriding the version number via the environment
variable SETUPTOOLS_SCM_PRETEND_VERSION

- fix issue 63 by adding the `--match` parameter to the git describe
call and prepare the possibility of passing more options to scm
backends

- fix issue 70 and 71 by introducing the parse keyword to specify
custom scm parsing, it's an expert feature, use with caution

this change also introduces the setuptools_scm.parse_scm_fallback
entrypoint which can be used to register custom archive fallbacks

- Add `relative_to` parameter to `get_version` function, fixes 44 per 45.

- fix issue with setuptools wrong version warnings being printed to standard out. User is informed now by distutils-warnings.
- restructure root finding, we now reliably ignore outer scm and prefer PKG-INFO over scm, fixes 43 and 45

- correct the url to github thanks David Szotten
- enhance scm not found errors with a note on git tarballs thanks Markus
- add support for `write_to_template`