Adding package.json and removing node_modules

Most other node.js projects use a `package.json` to list dependencies.  The `node_modules` directory typically is not committed.  This also could help address issue #1 so you only need to `npm publish`.

Installation of js2js would be one of the following.

```
# Option 1, use npm (after you publish it)
npm install js2js

# Option 2, use git
git clone https://github.com/eleks/js2js.git
cd js2js
npm install
```