Adds `createPartials` flag to generate docs as HTML partials.

- Adds `createPartials` key to data object that is passed to `jade.compile`.
- Adds docs for `createPartials` to command line help.
- Adds tests and fixtures for `createPartials` flag.
- Updates README.markdown with docs for `createPartials`.
- Updates `cmd.js` to accept `--createPartials` flag.
- Updates jade template to conditionally output full HTML or HTML partials.