HTML5 compatibility

This is a follow up to [pull request #18](https://github.com/lokesh/lightbox2/pull/18).

After @adymorz added data-lightbox as replacement for rel="lightbox" I reajusted a few things:
- User can choose HTML5-comptabile data-lightbox attribute or continue to use rel="lightbox"
- To group images to albums you can use data-lightbox="album" or rel="lightbox[album]" even interchanged
- Synchronized changes back to the coffe script (also I did not test the outcome ._.)

Maybe this could be a user-friendly way to add HTML5 support without breaking compatability.