Enhance ScrollDetector to use different reference points for 0 and 1

[75th]

Right now, ScrollDetector output is 0 when the top border of the reference element aligns with the bottom of the viewport, and 1 when the bottom border of the element aligns with the top of the viewport.

During development of my last site I had a thought that it would be nice to optionally make 0 and 1 be top/top and bottom/bottom instead. The big problem with that, though, is that the order of those times can be [ forwards / simultaneous / backwards ], depending on whether the reference element is [ shorter than / the same height as / taller than ] the viewport.

Also, maybe there's a case for using different, arbitrary points altogether? All this needs a lot more thought

[75th]

The confidence-shattering basicScroll library I learned about too late has [top|middle|bottom]-[top|middle|bottom] keyword values. All aboard the RIPOFF EXPRESS