Reason: The `script/delayed_job` process (described above) uses the
[Daemons](https://github.com/thuehlinger/daemons) gem which has several
undesirable behaviors when running inside a container (Docker, etc.):
- The parent process spawns a background child process then exits immediately,
which causes the container to shutdown.
- The worker processes are detached from the parent, which prevents logging to `STDOUT`.

The `--fork` option solves this by running workers in a foreground process tree.
When using `--fork` the `daemons` gem is not required.

The command script requires changing the following line to enable this:

# always daemonizes, never forks
Delayed::Command.new(ARGV).daemonize

must now be:

# daemonize by default unless --fork specified
Delayed::Command.new(ARGV).launch

In addition, there are several quality of life improvements added to the Command script:
- Command: Add --pools arg as an alias for --pool, and allow pipe-delimited pool definitions
- Command: Add --num-worker arg as an alias for -n / --number-of-workers (and deprecate --number-of-workers)
- Command: Pool parsing code has been extracted to PoolParser class
- Command: Add -v / --verbose switch which sets quiet=false on workers
- Command: Add -x switch as alias for --exit-on-complete
- Command: Add STDERR warning num-workers less than 1
- Command: Add STDERR warning if num-workers and pools both specified (pools overrides num-workers as per existing behavior)
- Command: Add STDERR warning if queues and pools both specified (pools overrides num-workers as per existing behavior)

The Rake script has also been enhanced:
- Rake: Uses Forking launcher under the hood
- Rake: Add support for NUM_WORKERS and POOLS args

- Add validation of min vs. max priority

…king-launcher