NPM package, Common.js and Require.js/AMD support

Hey James,

I've added a few thing in this pull request:

* A `package.json` file for publishing to NPM as a package.
* Support for Common.js and Require.js/AMD.
* A `minify` script that automates the minification and gzipping of the `satisfy.js` script using closure compiler.

Please let me know if you want me to update anything in this commit. I've left the version at 0.3 for now in both the `package.json` and the license comment in `satisfy.js` but you'll probably want to update that.