Slide volume

Tracker 4.44

### 10 Slide volume

If phi is not null slide the volume up by phi each tick, else slide the volume down by plow each tick. Note: phi and plow can be zero, there will simply be no volume change.

A good test is the module ``ghouls and ghosts`': if you mix up the test for phi and plo, you won't hear the flute solo.

Scrolling mode:

         1 A-4 vol +5

sample number / note / slide increment