Major MIDI2CV Mk2 upgrade

MIDI2CV Mk2 got some long overdue overhaul with firmware version 3.0! Here are the most noticeable changes:

The rarely used DRUM mode was replaced with POLY mode that provides true polyphonic voice allocation for up to 4 voices.

MIDI I/O code was reworked resulting in complete elimination of gate jitter: delay between MIDI Note On event and GATE signal is now constant 290us. This also significantly improved soft MIDI THRU which now also has constant delay from MIDI IN.