Create custom Rake release task

[hferentschik]

On top of the existing release task, this task should:

• Update the CHANGELOG (based on a given milestone)
• Set the right release version (interactively and via command line flags; think mvn release)
• Push commits
• Run the existing release task
• Set the new dev version
• Push commit

The idea is that provided that one gives all required information either via cli options or interactively, the whole release process is automated. This allows then also to so a release via a CI release job.

[hferentschik]

We can use this gem to talk to GitHub - https://github.com/piotrmurach/github