Implement versioning using commit hash

[lobis]

Right now versioning is using a version file which contains a string of the form 0.0.1. On each execution of the materials.py script this version is increased and included into the xml version tag.

We should define an additional tag (commit?) to store the commit hash information into the generated materials.xml. This could probably be done using git hooks.

Relevant discussion: http://ezpc10.unizar.es/t/important-material-repository-updates/460/12

[jgalan]

However, there might be material files that are managed manually. They will also be automatically stamped with a version?

I believe, for the particular case of restG4 you could just integrate that at TRestGDMLParser, reading it from https://sultan.unizar.es/materials/.git/FETCH_HEAD which is synchronized with this repository.

[jgalan]

This command should do the job:

git ls-remote https://github.com/rest-for-physics/materials HEAD