Rewrite sndvol32 with code from MixerPlus

MixerPlus is an alternative implementation of sound mixer application written in C by John Peloquin and released under GPLv2:

https://github.com/blargoner/mixerplus

It works perfectly in Windows NT 5.x environment and, basically, all it needs is a GUI redesign to resemble standard Windows sound mixer, as well as a snippet of code to work as systray volume control.

It's better than current ROS's sndvol32 in terms of stability and usability:

• works properly and does not crash on Windows NT 5.x
• precise volume controls instead of chunky stepped one from ROS's sndvol32
• allows to auto-fade in and fade out each channel
• allows to crossfade between sound sources
• allows to separately control volume for each channel (L & R)

As an alternative, it can be included into RAPPS downloads.

Attached the archive with latest GitHub source code snapshot and compiled binary in "Release" directory.