Improve std.algorithm.find overload docs

* Group element-wise find overloads together.
* Properly document Boyer-Moore find.
In that case, I'd say that the glossary needs to be updated. I'm not sure what to do about other occurrences of "input range", etc., because in theory, they should *all* link to the glossary so that a newbie can look up what the terms mean. That would make the documentation more useful than it is now.