move argument parsing to Click, or twisted.python.usage.Options

[warner]

We're currently using argparse for CLI argument processing, but I'd like to move to Twisted's native argv-parsing code (twisted.python.usage.Options). The two goals are:

• remove a dependency (we're already depending on Twisted anyways)
• add aliases, so wormhole rx does exactly the same thing as wormhole receive (I keep forgetting how to spell "receive" when doing a demo, how embarrassing!).

[warner]

When I asked, Glyph seemed uncertain whether he'd recommend t.p.usage.Options or click. So it might be a good idea to investigate Click and see how it'd look if we went that way instead.

[warner]

@meejah is working on this in #47

[warner]

#47 got landed, so this is done. There are some lingering bugs (--no-listen) seems to be stuck on, for example), but overall it's looking good.