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
semver's error messages are not super user friendly:
```
$ ./gitsem patc
2014/08/29 13:05:01 No Major.Minor.Patch elements found
```
Maybe consider printing a nicer message ("version must be one of major, minor, patch")? Up to you.