device.hardware: nudge the operator to reflash obsolete devices. Fixes #239. Closes #247.

device.hardware: check if device is busy before loading firmware. On Linux multiple userspace applications can send control requests to a device without being aware of each other. Claim every interface to ensure mutual exclusion with any other application. On other OSes device access is already exclusive. Fixes #241.

target.hardware: whitelist `PROCESSOR_ARCHITECTURE`. It is used by wasmtime-py to determine which DLL to load. Fixes #383.

applet.video.ws2818_output: make @attie code owner

applet.video.ws2818_output: support different input vs. output pixel size

applet.video.ws2818_output: add support for LEDs other than RGB

applet.video.hub75_output: implement basic HUB75 test pattern generator

software: fix typo.

README: add comment about applet entrypoints and re-running install

support.plugin: generalize from applet.metadata. At this point we have at least three subsystems that would benefit from a plugin mechanism based on entry points that was added to handle applets: * Applets. Duh. * Applet tools. Currently very awkwardly attached to applets even though they aren't really related. * Data loggers. `support.data_loggers` depends on `aiohttp` for a part of its functionality but because there was no way to express it, a data logger specific work around was added. This commit lays the foundation for using the same plugin system for all three.