Updated copyright, LICENSE and added a README

Mass change Shebangs

Started using pipenv and added LICENSE

Make the mystery ship spawn

Make the last ship alive move to each end of the display

Initially add the alien horde which fires at the tank

Fix logic error prompting to shoot ships when they shouldn't

Added the mystery ship which flys across the screen

Massive overhaul

explosion.py now uses the Animation class

Ships are now animated. Time based operations now use seperate variables.

Additional refactoring by removing extra ship classes

Started refactoring by removing some classes

Reordered constants

Added explosion sprites. Started adding alien ships.