envy24control midi updates

envy24control midi updates
I have enhanced the midi control of envy24control.

1) I have fixed midi feedback, where issuing a controller event resulted in
the controller value beeing sent to the midi port again.

2) I have added midi controllers for the "mute" buttons, which can now be
controller via midi.

3) and while rewriting the midi code to support the mute buttons several
off-by-one errors have been fixed.
From: Dirk Jagdmann <doj@cubic.org>