gitRepo: Improve the packaging

Improvements:
- Use a versioned URL
  - The build won't break anymore (due to a wrong hash) after a new
    version is being released
  - It will be possible to build older versions
- Add (hopefully all) runtime dependencies (Git, GnuPG and less (for
  "repo help"))
- Add the upstream license
- Add a long description
- Use the name of the Git tag for the version
  - The version number from the script (currently 1.23) is only
    incremented after "important" changes (i.e. there are slightly
    different different scripts with "VERSION = (1, 23)")