Overwrite repo keywords

Considering that only repo-compliant packages can be
uploaded, there should be no harm in being able to
overwrite keywords during updates.

This toolkit is just to simplify things in a controlled
way. If a user wants, he can do manually copy files etc.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Release 0.0.6

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>