* Added "show_upgrade_diffs" script
"show_upgrade_diffs" pulls a git directory and a user branch from nomulus and
compares all of the versions of all dependencies specified in all lockfiles in
the master branch with those of the user branch and prints a nice, terse
little colorized report on the differences.
This is useful for reviewing a dependency upgrade.
* Add license header
* Changes requested in review
* Changes for review
- Change format of output so different actions are displayed somewhat
consistently.
- Make specifying a directory optional, if not specified create a temporary
directory and clean it up afterwards.
