tool to manage git semantic versioning for git repositories 

the README is basically copy+pasted from npm version, right now

One thing I struggled with was if it was better to exec git directly or use the [official Go bindings for Git](https://github.com/libgit2/git2go).

Pros of official bindings:
  - better Git integration with Go (actual errors vs only exit code + parsing stderr)
  - not dependent on consumer's git version in case of changing git API

Cons of official bindings:
  - requires building and linking libgit2 into the binary
  - lots of commands we don't want or care about, further swelling binary size
We accept arbitrary version strings here, if they don't do patch/minor/major. Maybe we should wrap the error from semver, so this would look something like: "failed to parse patc as semver: No Major.Minor.Patch elements found"

Thoughts?