Add a CLI so you can `cat package.json | npd > package.json`

I like the idea of [cleaning up my package.json locally](https://github.com/npm/normalize-package-data#what-normalization-currently-entails) so I can learn to be a better npm citizen and write better package.json files. To this end, I've add this CLI that reads from `stdin`, normalizes, writes to `stdout`.

A few concerns:

- Maybe there's already a tool that does this?
- I gave the CLI two names: a long one that matches the package name, and a short one (npd) that's easy to type. I like this flexibility, but maybe it's Bad™
- Is there a way to detect the absence of stdin, so usage can be displayed if the command is run without having anything piped to it?