Bumpv

- bugfix: Read only tags from <span class="title-ref">git
describe</span> that look like versions

- bugfix: `--help` in git workdir raising AssertionError
- bugfix: fail earlier if one of files does not exist
- bugfix: `commit = True` / `tag = True` in .bumpv.cfg had no effect

- **BREAKING CHANGE** The `--bump` argument was removed, this is now
the first positional argument. If you used `bumpv --bump major`
before, you can use `bumpv major` now. If you used `bumpv` without
arguments before, you now need to specify the part (previous default
was `patch`) as in `bumpv patch`).

- add --no-commit, --no-tag

- If available, use git to learn about current version

- Mercurial support