Improve std.algorithm.find overload docs

* Group element-wise find overloads together.
* Properly document Boyer-Moore find.
Firstly, *forward range* doesn't exist in the glossary. *Input range* exists but doesn't have an anchor, and it is out of date (it uses "empty, head, and next"). Also this is the only std.algorithm function that links to the glossary, despite *input range* being used both before and after this overload.