Adding sound

Now I have added the collision to the Game in those functions I will be able to sound to them.
I have kept the Same sound for alien collision with bullets and astroids with bullets, this sound is an exploding sound.

Sounds added:

• alien and bullet collision
• astroid and bullet collision
• Spaceship Death / losing a life
• Coin Pickup
• Diamond Pickup
• Background Music 

Background Music has been added, the music is theme in a retro feel which goes with the rest of the theme.