Fix default shutdown of child supervisors to infinity

A supervisor should wait for a child supervisor to shutdown its
children, and not kill it. By killing a supervisor you may prevent the
correct termination of processes further down the supervision tree.
Merge pull request #1546 from fishcakez/supervisor-shutdown

Fix default shutdown of child supervisors to infinity
Document dash to underscore in OptionParser
Make it explicit Regex.run returns all captures in a match
Original clean arguments need to be passed to deps.clean.
Test mix clean with the --all flag.
Merge pull request #1554 from tristanoneil/mix-clean-all

Pass clean arguments to deps.clean