Miditk-smf

Fixes:

- Fixed writing polyphonic pressure events in `MidiFileWriter` (16).

Thanks to Jared Boone (jboone) for the fix.

Project updates:

- Oldest supported Python version is now 3.8.

Project updates:

- Switched from `setuptools` to PEP-517-compatible build setup using
`hatchling`.
- Removed Python 2 support (now requires Python >= 3.7).
- Removed `six` dependency.
- Removed requirements files.
- Converted README, LICENSE and CHANGELOG to Markdown format.
- Added automatic testing and deployment of source distribution and
wheel to PyPI via GitHub actions.

Changes:

- Made `track` argument to `BaseMidiEventHandler.start_of_track` optional.
- Split `MidiFileWriter` into base class and event handler sub-class.
Base class handles event serialization and output.
- `MidiSequence` instances now save tempo and time/key signature events.
- `MidiSequence.fromfile` can now accept a custom handler class/instance.
- Added command-line script `miditk-mid2syx`.
- Updated examples and removed Python 2 compatibility idioms.

Fixes:

- Fixed writing sysex message events in `MidiFileWriter` (7).
- Removed unused `dispatch_controllers` attribute in `BaseMidiEventHandler`.
- Fixed `MidiSequence` example in readme and added example script.
- Minor fixes: removed unused import; added geany project file to git ignores;
fixed code formatting issues.
- Reformated code with `black` and `isort`.

- Added example script to convert a type 1 MIDI file into a type 0
format file.
- Moved previously private `MidiEvent` class to `miditk.smf.api`
module and exposed it in `miditk.smf` module name space and improved
and fixed several aspects of the `MidiEvent` class.
- Fixed parsing of polyphonic pressure events.
- Fixed output for polyphonic pressure events in
`PrintingMidiEventHandler`.
- Fix time keeping in `ObjectMidiEventHandler` for multi-track files:
reset `current_time` attribute when new track starts.
- Fixed: `BaseMidiEventHandler` used wrong handler method name for
sysex messages.
- Updated base/dev requirements.

- Fixed missing string formatting args in
`PrintingMidiEventHandler.key_signature` method.
- Added `example_program_change_map.py` script to examples.
- Ensure support for Python 3.7.

- Removed Cython version of `miditk.smf.converters` module
(`miditk.smf._speedups`). `miditk-smf` now only requires `six`.
- Fixed `tox.ini` to work on Windows too.
- Improved and updated readme file.

Initial release