design update

Hi!

To improve try-haxe I created an update to prettify the application and make it more recognizable in style of haxe.org. Hope you like it :smile: 

* added haxe styled header with logo and links to docs
* add subline "the Haxe playground" because it sounds cool
* fonts in line with haxe.org website
* added example dropdown with 17 examples. I did this because I think people might want to play with Haxe somewhere before they even download it. This (should) gives them an first impression of some great features.
* added disclaimer: _The code you enter on Try-Haxe is compiled and saved on our servers._ 
* added favicon
* added about page with logo and download link
* made haxe source editor higher; more space to code in!
* renamed "link" button to "run standalone"
* hide fullscreen button
* added own FB-share image

The logo/images/favicon are hosted/linked from haxe.org, I assume they don't mind.
![try-haxe-update](https://cloud.githubusercontent.com/assets/576184/4714398/9b401c6e-58f1-11e4-8809-010d25789297.gif)