add argument parsing
add argument parsing

Now that 'command' is removed from .scuba.yml, the first argument passed to
scuba cannot be an option; it must be the command to run in the container.
This disambiguates options to scuba itself.

Right now, we just handle --help (from argparse itself) and --version.

JonathonReinhart/scuba,JonathonReinhart/scuba,JonathonReinhart/scuba