added options

Hi, we're trying to migrate the [nodeschool](http://nodeschool.io) workshops to use Markdown formatting on the commandline with msee but would like to be able to adjust a bunch of formatting options.

This PR adds an options object that lets us change some things (in particular I'd like to have more whitespace around paragraphs).

Cheers!

/cc @timoxley does this do enough for you too?