jQuery & SyntaxHighlighter update + codecode plugin.

Hey Addy,

While I was reading the book online, I thought of an idea for a small jQuery plugin which would simply clone a block of syntax-highlighted code, and `position: fixed`-it to the bottom of the page. That way, you can see the code the text is talking about, without having to scroll up, then down, then up, then down. It's something that has always frustrated me, and this simple solution just might make learning easier for a lot of people (myself included)!

I did a couple of things in this PR:

* upgraded jQuery to 1.9.1
* included the plugin, called [`codecode`](http://github.com/stephenplusplus/codecode)

To see the plugin in action, I created a `gh-pages` branch for my fork of `essential-js-design-patterns`, over [here](http://stephenplusplus.github.com/essential-js-design-patterns). Let me know what you think!