add package.json to support npm

@mattes

I know this is somewhat old, but I found it useful. If you'd like to take the time to [publish this module](https://www.npmjs.org/doc/cli/npm-publish.html) to the npm registry, I've added the necessary components for a baseline configuration. That way it will be more visible and accessible to others who may want to install it.

It might be a good idea to adjust the license to one your choosing, and add a LICENSE file. 

Thanks!