UI improvements.

I've added a bunch of new features to the UI, mainly using jQuery to try and make it a bit nicer.

The main features are:

* The output looks like a console.
* After each action is performed, a message is displayed showing the result.
* The errors are shown to the right of the code, and when an error message is hovered over, the relevant code is highlighted. This fixes #4, as error messages without code portions to highlight can still be seen.

**Note:** Some of these features may not work as intended or even at all on old browsers such as IE7 and earlier.

Some images are attached showing these new features.

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![New console with compilation success message.](https://f.cloud.github.com/assets/2750246/2059994/f0c9cf32-8bf0-11e3-9b36-dc093f63dbf3.png)

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![New error message display with compilation failure message.](https://f.cloud.github.com/assets/2750246/2059995/f50a8424-8bf0-11e3-85a5-5799b200a37d.png)

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![Code highlighting when hovering over an error message.](https://f.cloud.github.com/assets/2750246/2059996/f97f2582-8bf0-11e3-8a71-f856d4b2e43d.png)