Add version numbers to the toolbox

[venthur]

Adding version numbers will make it a lot easier to refer to a certain state of the toolbox.

If we use versioning, we can use git tag, and github will automatically create downloadable zip files for each version.

I propose a versioning scheme that follows the widely accepted standard MAJOR.MINOR.PATCH. An Increase of MAJOR signifies a backwards incompatible changes, MINOR for backwards compatible changes, and PATCH for small bugfixes. See http://semver.org/ for more details.