Release script improvement

Refactoring of the release script.

The script is to be called when a release has do be done. It follow the [classic gitflow] (http://nvie.com/posts/a-successful-git-branching-model/)  for release.

3 arguments are available:
* major 
* minor
* hotfix

The script branches from either ```dev``` (for minor and major) or ```release``` (for hotfix), change the version number, merge the  ```temporary release branch ``` into ```dev``` and ```debug``` and tag the  ```release ``` with the new version number.

For the moment it does not push the ```dev ``` and  ```release ``` branches to remote (you have to check that everything is ok before).
The hotfix part is under work, for the moment it only does the first part of the process (fetching, creating temporary branch and updating version number). After that you have to make the hotfix changes you want and follow the instruction in comment at the end of the script (to merge the temporary branch, tag, ...)