First set of exercises for Interacting with the user

The primary exercises in this set are the ones in "Command Line Arguments". There aren't a ton of them, but they are complete and read to go.

I drafted a set of exercises to go over STDIN and STDOUT using node's `readline` module. If they'd be useful, I can complete the set. It might be a bit too confusing though. Lots of room to get confused about how streams work.
I'd recommend adding another exercise which introduces [minimist](https://www.npmjs.org/package/minimist) to do argument parsing that supports flags and options.