This makes debugging configuration issues easier. When the file does not
exist, the absolute path of its expected location is logged.

Also moved from os.path to using pathlib.

The new task types are actually used by Flamenco Server.

This passes the current hostname and list of supported task types to the
manager.

This allows a finer granularity of task selection for a given worker.

This is now implemented for Blender renders, merging of EXRs, and files
copied using the 'copy_file' command.

These zips contain the Wheel, an example configuration, README and LICENSE
files, and system integration files.

Now "Flamenco-Worker/{version}" is used, instead of
"Flamenco-Worker {version}", to comply with RFC 7231 section 5.5.3
https://tools.ietf.org/html/rfc7231#section-5.5.3

This header is included with each request, so that the Manager can handle
software version bookkeeping however it sees fit.

Round away the milliseconds, as those aren't all that interesting.
Uniqueness is ensured by calling _unique_path().

The colons in the timestamp are gone, and numerical suffixes (to ensure
new directories are unique) are prefixed with a ~.