[pygame] Overall volume control for sounds

[Ivan DelSol <sunspider@xxxxxxxxx>]

I'm trying to write a system that has controls for overall sound
effect volume. There does not seem to be a way to control all the
sound channels... There doesn't seem to be a way to get pygame to pass
channels by ID so that I could alter their volumes individually, let
alone control the sound channels' volumes as a whole.

Volume control seems like a pretty standard need in a game. Anyone
else figured this out?