Python-rtmidi

Changes:

- Updated `rtmidi` submodule (156).

Project infrastructure:

- Updated `requirements-dev.txt` with `pip-compile` (153).
- Changed CI to build separate wheels for both macOS architectures (18bbc74, 20f5cdd).
- Improved build dependency selection in meson config (156).

Project infrastructure:

- Fixed broken windows binary wheels built by CI.

Fixes:

- Fixed memleak in `midiutils.list_{in,out}put_ports` function (103).
- Fixed compilation with PyPy3.

Documentation:

- Clarified return types in docstrings.
- Converted readme, changelog, authors, and install docs to Markdown.

Examples:

- Fixed `basic/panic.py` to actually use channel number loop var.

Project infrastructure:

- Modernized project structure and build system (now used `meson` and `mesonpep517`) (119).
- Added working cibuildwheel github action (121).
- Removed redundant Github action (140).

Fixes:

- Fixed Windows build for 64-bit Python 3.9 on AppVeyor CI.

Changes:

- The SysEx reception buffer size for the Windows MM backend was
changed from 8096 to 8196.
- Synced with upstream [RtMidi](https://github.com/thestk/rtmidi)
(3dc525baf3cac345cdd3511316571c20b47f30b5, fixes 89).

Fixes:

- Fixed Windows builds on AppVeyor CI.
- Fixed command line parsing in `midiclock.py` example script.

Changes:

- Release GIL in `MidiOut.send_message` so that on backend APIs
where this operation is blocking (`WINDOWS_MM`), multiple Python
threads using this method on different `MidiOut` instances can
run concurently.

Fixes:

- Fixed compiler deprecation warning about `PyEval_InitThreads` on
Python 3.9+.

Examples:

- Added `send_sysex` and `send_sysex_file` example scripts.

Documentation:

- Remove references to old project homepage URL and fix readme
badges.