Synthizer

These releases are a test series for moving CI to GitHub Actions. Though not user-facing, 0.8.14 now blocks on
successful Linux CI for Ubuntu 20 and thus gives Linux support which is on par with Windows.

The flagship feature of this release is [filters](../concepts/filters.md). Python users should see [the Python
tutorial](../python_tutorials/filters.md). Also:

- Synthizer now builds on Ubuntu 18.
- Python no longer eroniously exports top-level enums due to undocumented Cython behavior.
- If you were using ints as property values instead of enums or relying on the topp-level definition, you will need to
update your code. This was never intended to be part of the public API.
- It is possible to set generator gain before adding it to a source without triggering a crossfade. Internal changes to
the crossfade helpers should make bugs like this much rarer, and probably fixed others that were yet to be reported.

Release Notes for 0.0.x to 0.8.x

Starting at 0.8 and later, Synthizer maintains separate pages for every incompatible release with more details on
compatibility breakage and what specifically changed. The following were early development versions, and should no
longer be used.

This release is the long-awaited improved HRTF. This might not be the final version, but it's much better in quality
and the scripts to generate it are now much easier to maintain. Please leave any feedback
[here](https://github.com/synthizer/synthizer/issues/27). in particular, it is not feasible to test the entire sphere,
so it may be possible to find azimuth/elevation combinations which do weird things.

- Fix: non-looping BufferGenerator with a pitch bend is no longer silent
- Fix/improvement: In Python, Synthizer events inherit from a common base class.

- An [event system](../concepts/events.md). This is alpha, and changes are expected in 0.9.
- Add `SYZ_P_PANNER_STRATEGY` to Context to default panner strategies for new sources.

- Fix: the library no longer crashes due to internal races between handle deletion and execution of audio commands on
the background thread
- This fixes a number of crashes, most notably issue 50, which highlighted the issue due to effects relying heavily
on commands.
- Fix: streaming generators no longer spuriously seek to the beginning of their audio after generating the first few MS
of audio (issue 49)
- Fix: `panning_scalar` will once more properly take effect if set immediately after `PannedSource` creation (issue 52)