New method and function to handle scrolling for handleJSON

If $resp->scrollTo($sel[, $nth]) is given to handleJSON, it will do
document.querySelectorAll($sel)[$nth].scrollIntoView(). Need to use $nth (
default is 0) in cases where :nth-of-type($nth) would not work due to it not
handling larger numbers. In cases where you would use ('li:nth-of-type(600)'),
it does not seem to work, so use ('li', 600) instead.
Use $resp->scrollTo() to scroll to the newly loaded content

Assuming that it is the first-child of main, which it should be.

Scroll to the top of the article or whatever so that you do not have to scroll
there yourself or begin reading the middle of the content.