[Feature] Set sound volume

[compufox]

A method to set the volumes of sounds either at time of defining or time of playing (or through something more advanced like a sound mixer api) would be very much appreciated.

[borodust]

trivial-gamekit's goal is to be as simple as possible, so sound mixing is too much for it. I'll pour more thought into adding some basic sound effects though.

[compufox]

awesome! thanks!