Big performance improvements

* Updated hidpi detection rules.
* Lazy loading detection now works much better.
* Lady loaded images outside of the viewport's range are now unloaded
from memory.
* Breakpoint detection should now work more smoothly.
* Fixed some cases where image sources were being set to the same value
repeatedly.
* Reduced memory consumption.
* Various other misc performance improvements.
* Added experimental ADM support. Experimental in that I haven't tested
it at all yet.
Demo image optimizations.
Adding a sassy little demo of lazy loading.