Complete overhaul of the interesttarget explainer (#1141)

* Complete overhaul of the interesttarget explainer

This should bring it in line with all/most of the recent discussions. Hopefully I didn't miss something important, or butcher a concept that was previously better explained.

* Replace comment character

* Address comments

* Fix up links

* Few more tweaks, remove <input>

* Remove HTMLInputElement

Author: mfreed7