Initial documention for usage with webpack

[johnsusi]

Got webpack working with clearwater and might as well document the procedure. :)

[jgaskins]

This is great!

I want to address that issue requiring setting global.virtualDom. It's probably due to compiling virtual-dom with Browserify right now. I've tried a couple different things where I compiled the JS with Webpack/Babel, such as #48 and a couple experiments where I swapped out virtual-dom with inferno and snabbdom and used Webpack for all of that. Everything worked just fine when I tried it. I have no idea why it worked — maybe Opal requires play nice with UMD-style requires?

Anyway, if we move away from the Browserify compilation and merge in the Webpack config used in #48 (even if that PR itself isn't merged in), that problem might go away. I'll go ahead and merge this, though. 🎉

[johnsusi]

That reminds me; I used a virtual-dom from npm, not the one bundled with clearwater. That might be an issue if you have applied patches to it?

I think the main issue is that some javascript libraries detect if they are in a browser environment or not. Most libraries that I have tried identify that they are running under node when using webpack and thus use commonjs requires.

There is no way for webpack to figure out that require 'clearwater/virtual_dom/js/virtual_dom.js'
should be transpiled to global.virtualDom = require('./clearwater/virtual_dom/js/virtual_dom.js').

I'm new to webpack so there might be some way to configure webpack to solve this.