Avx

It's here, the long-awaited v1.0.0 release of avx.

No changes from v1.0.0-rc1, other than the version number.

This project adheres to semantic versioning, so from now on any backwards-incompatible changes will mean a v2.x release.

Release candidate for avx v1.0.0 (at long last)!

Some fairly hefty breaking API changes in this version, including:
- Serial listener classes have been removed, and serial devices now have built-in listener functionality. See 65.
- A cross-client and controller-to-client messaging system has been added, replacing the implementation-specific functions that had been included in the `Controller` class. See 66.

Will leave as RC until I'm confident that nothing else breaking needs to happen (essentially until I've updated https://github.com/staldates/av-control to use it and it all works).

Changes in this version:

- Use `threading.Thread` directly rather than `Pyro4.threadutil.Thread` - the latter has gone away
- Limit commands sent to ICStation relay cards to one every 0.1s
- Add a MomentaryUpDownStopRelay class

Changes in this release:
- Client list is persisted across restarts if the config file is writable by the avx-controller process.
- Bugfix: remaining active clients weren't being called from `callAllClients` if an inactive client is found before them in the list. This is now resolved.

Notable changes in this release:
- New `LogEvent` added to `Sequencer` to add an entry in the controller log
- Increased support for ETC Unison lighting controller
- Added support for manual exposure control functions for VISCA cameras
- Removed legacy `VISCACommands` module
- Added environment variable `PYRO_IP` to override detected host IP
- Improved test coverage

avx is now also available on PyPI.

Minor bugfixes and quality-of-life enhancements:
- Bug in removing of dead clients fixed
- Device-specific functionality moved from `SerialListener` to specific subclasses
- Support for custom logging configuration added
- Unused and implementation-specific `StringConstants` class deleted
- Controller startup and shutdown is now logged