Add music and sound effects

[felipenmoura]

We should have some low song in the background, perhaps also a fire or rain sound, and of course, the sounds for events:

• letter typed
• correct word
• hit (success)
• hit (failure)

[suleka96]

I worked on this and added sound effects for success, failure, final win and input of correct word. I hope the sound effects are suitable for the game environment. #8