updates for npm and browserify

I have a project for node.js called [browserify](http://github.com/substack/node-browserify) that provides browser-side node.js-style require() for bundled-up javascript directories and modules on [npm, the node package manager](http://npmjs.org/). This patch adds a `package.json` so that the module is ready for publishing on npm and a `browserify.js` so that you'll be able to require('jquery-mousewheel') browser-side with browserify like the readme details. Once you have npm (and node.js) installed, just do
    npm publish
from the jquery-mousewheel directory and then anybody will just be able to `npm install jquery-mousewheel`!

I can publish this to npm too if you don't want to install npm or node.js or you think this patch is silly. Thanks for the nifty plugin!