#3 Calibrated volume/power translation tables

[yki]

Currently, the XM volume levels do not translate to OPL4 output levels properly. The levels have to be calibrated with some sort of measurements, so that "what you hear in XM tracker is what you get on MSX/OPL4". Once the correct transfer curves have been found, it should be possible to code them in the pre-calculated volume tables that are already in the player.