Heavy update

Here is a heavy update of the game.

1. New music. Music by TeknoAXE.
   
   1. Enraged Hillbilly;
   2. Finding a Way Through the Sludge;
   3. Until Your Engine Stops;
   4. Until Your Engine Stops II;
   5. Cranked to Eleven;
2. New balance. Now ammo kits and med kits drop less frequently.
3. Some slight bugfixes.