Switch bundling system to Webpack

Just for kicks I wanted to see how involved it would be to switch to Webpack and it turns out to be incredibly simple. Webpack has better support for SourceMaps and it even generates a smaller minified bundle than Browserify.

I updated the `dev` & `build` tasks to use Webpack. `dev` compiles with SourceMaps & watches all the modules for changes. `build` compiles once and minifies with UglifyJS.