Set Parallax to body

[antokhio]

Hi, guys, thanks for great lib, came here from this question and this issue

Are you proposing that Parallax be able to set its container to body

Seems to be exactly a feature request the library or documentation lacking currently
The problem is quite obvious, when i apply parallax resulting height of body is "0", witch is going to break "standard" way of dealing with Header, Footer, Modals bodyLock, anchor navigation .

And the second problem also that, pages are always 100vh witch is kinda hard to maintain unless you have full screen slides.
I thought to useMeasure on sections and calculate factors from that, but this seems to be an overkill, and i think 'factor' is also memorized so you can't provide it dynamically.

Idc, i can try to assemble some PR's to try add this stuff, but i would like first to know are there any opinions, since this probably two the most hot features to add.