Add some CLI options

[Announcement]

-v now prints the current version number. -h now display a simple help message.

Implements feature request in issue #407 raised by @SheetJSDev

[revin]

Hi @Announcement thank you, this is awesome 🎉 🎉 🎉

The Travis build is failing because of the standard formatter stuff complaining about a couple of unused variables. Do you think that's something you'd be interested in taking care of? I can totally take it over too if you'd rather do that; just say the word.

✨ Thanks so much! ✨

[bcoe]

@revin @Announcement would you be open to pulling in yargs for this? it gives nice pretty output, and will scale better as we add more configuration options.

[revin]

@bcoe 100% in favor of yargs; I'd love to have better CLI configurability, so whatever makes that easiest

[nextgenthemes]

So this has no CLI options at all. Is there a config file it reads? No docs, nothing. Hours of searching for something as simple as running some super basic markdown to html in npm scripts with a modern lib like markdown-it and landed here because it does not seem to have a CLI ...

4 years and not even the most basic switches get pulled. Official NPM thing??? I basically just want it NOT to remove classes from HTML inside the markdown. Any package suggestions?