DIGIDREAM additional notes

Special Thanks to fenarinarsa because:
- the music is encoded with the PYM ("Pattern YM") format, largely inspired by his FYM format used for "Latecomer".
- He exhumed the "AN3 forgotten trick" from Jim Sather's book Understanding The Apple IIe.

This feature, described by Jim page 8-24, was probably never used (or a very few times and probably a very long time ago). 
It only works with NTSC or PAL mode (not with RGB output). 
It allows you to instantly switch orange color to violet and blue to green (and vice versa) without having to redraw anything!
Used in conjunction with a simple page change ($C054/$C055) like here, this allows you to have the 4 colors of HIRES mode on the same portion of the screen without redrawing one single plot. Indispensable here because playing the digidrums takes almost all the CPU time available.
"AN3" is the name of the switches ($C05E/$C05F) to activate to make the change appear!


Trivia: Sharpness Buzztone is one of the first YM I tried to play on an Apple II when years ago (OK actually... 2015), I did my first YM player tests. 
I quickly gave up, the track seemed too huge for an Apple II (the decompressed YM is more than 300KB) and the presence of digidrums quickly aborted my tests at that time.

The "PYM" format makes it possible to reduce the size to 17KB (without counting the digidrums) and my learning of the INTERRUPTS' powah finally allowed me to be able to play this song on an Apple II!