1. Added sound: bg music, menu navigation sfx, player death sfx, skills
sfx, etc.
2. Fixed a bug where enemy sprites would not be removed from memory when
they exited the view
3. When activating the Warp skill you can now see how long you have to
Warp before it is canceled
4. When activating the Force Field skill you can now see how long you
have until the shield breaks/timeouts
5. The Energy bar will not appear if the player hasn't invested any XP
in skills
6. The Energy bar now shows the exact point at which the player can
activate Force Field or Warp (provided the player has at least one point
in either skill)