Created a little gold effect that shows up and fades out whenever an enemy is killed

-Created FadeOnce.cs, which derives from Fade
-Added a bitmap font to draw text via SpriteBatch
Created Multiple Game Levels

-Made it so that levels will end after a limited amount of time
-When levels end, made a "Level Complete" screen appear
-Made the "Level Complete" screen bring the player to the Shop when the "OK" button is clicked
-Added a "Done" button to the Shop, which brings the player to the next level
Merge remote-tracking branch 'origin/LevelTransitions' into GoldEffect
Merge branch 'GoldEffect'