added some menu functionality and two new weapons to enemies.

Added mainmenu, (newgame button will not reset game state.)
Added Highscore list, will be read and written to file.
Added Gun clas which acts as a bullet factory.
Enemies have randomized guns (three variants, straight shot, shot in player direction, and triple shot)
change damage to be on entity instead of bullet in order to do ship-to-ship collision damage.
Modified PlayState to use state variable to change render and input mechanics.