(#80) - Use nomnom for argument parsing

Why the switch
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1) optimist [has been deprecated](https://github.com/substack/node-optimist)
2) As part of #72 I'm likely to add new options soon (ones for cors e.g.) Having usage info in 2 places instead of three is handy then.
3) As part of #72 this project will become more complicated. Things like binding to a new port/ip while running need to be supported, as well as changing the PouchDB object while running. Less global variables and validation of these variables later on will definitely help then. Nomnom helps in both cases.
Splitting the usage strings would become very messy, even more since adding newlines would stop 'wordwrap' from working. I decided to just turn length checking off instead.