I have little changed functionality of the handling when auto loading is triggered

I have little changed functionality of the handling when auto loading is triggered. Now you can specify the element where the height should be checked. The benefit of this change is that you can, for example preload some data on server and jscroll just continue form there. To do this of course you have to enable jscroll on different (broader) element that if you would leave the library to do it from scratch.

Please contact me if you still find this unclear.