Make it work with Closure Compiler's ADVANCED_OPTIMIZATIONS

Hey there,

I refactored html5slider to be able to work with [Google Closure Compiler's ADVANCED_OPTIMIZATIONS](https://developers.google.com/closure/compiler/docs/api-tutorial3). This requires some rather unintuitive changes, so I'd understand if you didn't want to merge it upstream, but here goes nothing. :)

Thanks for the library!

Adrian