Release and branches workflow

[ericpre]

Now that we had a few releases of rosettasciio, it may be worth thinking of the branch structure and corresponding release/versioning.
So far, the release were made from the main branch and haven't been making any bugfix only release. I think that this works well and avoid maintaining several branches.
As mentioned in #275 (comment), considering the nature of rosettasciio, I am not sure that we would need bug fixes only releases and we could do minor releases, which would include enhancements/new features along bug fixes.

I think that the release process of rosettasciio should have the following characteristics:

• release often:
  • bug fixes and new features should be available quickly
  • contributors have clear expectation on how quickly their contribution can be widely used
• ease of release to be able release often
• don't break API without being clearly communicated:
  • it should be clear to users whether they can easily use a new release or if they need to check for break.
  • it should be easy to figure out from the release notes, when a bug was fixes and a new features or enhancement was implement and breaking changes occurs