Can go from main menu to select weapons menu and back again. Implemented
the Button class to make things simpler and consistent. When in play,
can press p to pause the game and a pause Menu will show with the option
of going to the main menu or returning to the game. It seems to return
back to the previous state, but "bullets" that have not "finished
exploding" do not continue on their route. Not sure if this is fix-able
or just avoid pausing when someone is firing. Will probably change the
buttons, but for now they'll work. Need to add a title to the main page