Rewrote the explosion sound to be more optimized and to be more dynamic.

* Explosions that are close to you play the usual sound.
* Explosions which are far away will play explosionfar.ogg, but with volume changed depending on the distance.
* Max cap (3, 7, 14) bombs will play explosionfar.ogg for half of the station (140 tiles).
* Explosion sounds will have panning, so stereo users will be able to tell the direction that the sound came from.
* Small bombs will play much less than max cap bombs, and be quieter.