Added a splash screen

-Added the Corundum Games logo
-Added a neat sound effect
-Updated the GSM to make our first state the splash screen
Added music to all the game screens

-Added music to the main menu that keeps playing in the Settings and High Score screens
-Gave one piece of music to each of the three game modes
-Gave the HighScoreState its own music to play, but only if we just finished a game
-Added a function to config to simplify playing music
-Also added a config.show_fps() function to cut down on long lines
-Added a ship firing sound effect and a cursor beep sound effect
-Finally, better separated constants, groups, functions, etc.
Merge branch 'master' of https://github.com/CorundumGames/Invasodado