Closes #53 - Add music
#52 - Coin sound effect.
Reorganize audio files.
#52 - Menu tap sound effect
#52 - Countdown sound effect
#52 - Tutorial sign sound effect.
#52 - Enemy attack and death sound effects.
#52 - Platform movement sound effect.
#52 - Commander attack sound effect
#52 - Runner sound effects.
Closes #52 - Change countdown and add game start/end sound effects.
#52, #53 - Added config setting to mute all sounds.
Merge branch 'audio'