Improve the development/contribution/build/release process

[Potherca]

Currently there is only a very short note on contribution ("don't forget to send me patches") in the documentation. The current build/release process needs to be documented (and possibly improved).

Suggested Improvements

• Use a CHANGELOG file to tag releases - Add a CHANGELOG #52
  Once a changelog is created as part of the process, it should be used to tag releases git tag -F <some-release-notes>
• Use a newer PHPUnit version (v4 instead of v3) -- Update readme + composer requirements; move license file and drop bui… #43
• Anything else?