[RFC] Semantic Versioning

I've been thinking a bit about changing Rugged to use Semantic Versioning.

I tried to follow the libgit2 version number in the latest Rugged releases,
but that's not been working out really well. One thing that is a bit bugging
me (and probably other users) is that Rugged releases are very infrequent and
inconsistent, and I'd like that to change.

Now, I'd like to move to a more consistent versioning scheme and follow
the guidelines of SemVer.

Here's a short rundown how I imagine this would look like:

• Development against libgit2 from git will happen in the master branch,
  as it does right now already. Beta releases will be cut from there and their
  version number will either be MINOR+1 or MAJOR+1, depending on whether
  newer changes break backwards compatibility or not.
• We'll keep maintaining PATCH releases for MINOR versions for as long as
  the matching libgit2 version receives updates.

Any comments or concerns?

No files, tests, or entry points are named. Start by reviewing Rugged's existing release process and how releases track libgit2. Done means agreeing on and documenting a Semantic Versioning policy covering master, beta releases, and maintained patch releases.