olcPGEX3_Miniaudio issues #318

I found some issues while using the extension in my little beat-maker game:

1. Sound doesn't have copy/move operations: This caused storing sounds in a custom container I had (which took the elements by value) to fail due to a double-free.
2. Sound has a voice pool yet you can't take advantage of it 100%: SetPitch/SetVolume/SetPan sets those parameters for all voices at once, so if you want to play the same sample with random pitch/volume (say you want to add variation to a pistol sound), you can't do it currently. I propose adding pitch and volume parameters to Play so you can set those on the voice it's about to be played.
3. Playback piles up when the window is unfocused, causing the queued sounds to play all at once in a loud burst when you focus it again, also we have EnableBackgroundPlayback which could be used (but it is not)