Add support for prefixed version tags in scc

With this commit, we sould now be able to tag the repository using
semver's recommended vX.Y.Z-METADATA. `get_git_version` has been updated to
recognize this new format so that both `scc version` and `python setup.py sdist` should work fine.
Add failing tests for wrong version numbers
Fix failing version tests
Add match argument to git describe
Merge pull request #144 from sbesson/version

Add support for prefixed version tags in scc