v1.1: MIDI and misc fixes and drum machine, kinda

New in this release, both available as UF2s below

picotouch_synth "app":

• MIDI in/out: use it as a MIDI controller both via USB or TRS-A MIDI
  • MIDI out: board acts like a standard MIDI controller (all "piano" keys send MIDI notes, oct up/down buttons transpose)
  • MIDI in: board receives MIDI on all MIDI notes and plays appropriately
• Misc adjustments to patches, including:
• patchB is now fatter with subosc detune

pts_drum_machine "app":

• First cut at drum machine, currently a sample player with 3 drum kits @ 11025 Hz sample rate (to fit on std Pico)
• Choose different kits with the A/B/C buttons
• Sends and receives MIDI
• Only the bottom row of the "piano" keys trigger samples, and only 8 samples per kit (at the moment)
• Use your own samples (mono 11025 Hz), see drum_wavs folder for layout