This makes it possible to start Flamenco Worker at Blender Studio with
a worker-local current working directory, with the executable in a shared
filesystem.
Within the shutdown procedure, signing off is now the last thing the
worker does. This makes things more consistent from the Manager's point
of view (like receiving last-second log entries while the Worker is still
online).
Completely flush the upstream buffer at startup, before attempting to
fetch a new task. These updates could impact any task on the Manager side,
and first flushing the buffer before appending new updates also seems
like a good idea.
Move the UPnP/SSDP Manager autodiscovery code into from `main.go` into the
`worker` package. This also means changing the error handling a bit, as
only the `main.go` file is allowed to do `log.Fatal()`.
The add-on code was copy-pasted from other addons and used the GPL v2
license, whereas by accident the LICENSE text file had the GNU "Affero" GPL
license v3 (instead of regular GPL v3).
This is now all streamlined, and all code is licensed as "GPL v3 or later".
Furthermore, the code comments just show a SPDX License Identifier
instead of an entire license block.
