Mobileer ME1000 synthesizer engine
Copyright Phil Burk / Mobileer, Inc.

The source in src/spmidi/ is the Mobileer SP-MIDI synthesizer by Phil Burk, from
https://github.com/philburk/mobileer-synth (commit bb1ec40), released under the Apache License,
Version 2.0 (see LICENSE). The individual file headers still carry Mobileer's original 2002-2007
"PROPRIETARY and CONFIDENTIAL" notices from when the engine was licensed commercially (Palm Treo and
other phones); the repository's LICENSE now covers them.

The ringtones in ../../sounds/mobileer/ are Phil Burk's, from the same repository
(data/ringtones/phil/), under the same licence.

Changes made for Backpack Defender: only the files needed for ME1000 MIDI-file playback were copied.
One line was added to engine/spmidi.c: "#undef assert" before its own no-op assert macro, because the
ESP32 toolchain's newlib already defines assert (otherwise a redefinition warning). Nothing else was
changed. config/spmidi_user_config.h (ours) selects ME1000, mono and static allocation.
