Python 3 support

* Change all 'print's to 'print()' and add the print_function future
  import to the files that use it.

* Import the configparser module as ConfigParser if we don't have
  ConfigParser (which was renamed in python 3).

* Change the imports::

  - We have no module named 'colors' when this package is installed, it
    needs to be a relative import to the root of the package, so use
    ''from . import <module>'' to get this done correctly.

  - Change the colors imports to explicitly say 'colors.rwrap' or
    'colors.gwrap'

This should allow supernova to run flawlessly in a python3 environment.