Made sound volume affected by atmosphere.

A played sound now has a range modifier (which can be disabled) based on the atmosphere of the tile.
At 101.325 and above, the sound plays at full range. Below that, the sound plays in 10ths of the original range for every tenth of the atmosphere, and in space sounds from a source don't play at all.

Only current issue (which is, as far as I know, impossible to fix) is that airlocks make no sound the first time you open them as there's no air on their tile. They make sound after that.

Should stop sounds playing if the source is in space.
Sound can still jump gaps in space, because otherwise this would require A* or some kind of pathfinding to do.
Changelog now.
Should the check be if (turf_source.zone.air) ?