python-docopt: new package

[Thomas:
  - Remove dependency on python || python3, as we did for all other
    python modules that work with both Python 2 and Python 3.
  - Rewrap help text.
  - Add <pkg>_LICENSE_FILES value.]

Signed-off-by: Alvaro G. M <alvaro.gamez@hazent.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>