Doc and lispref updates related to searching

Doc and lispref updates related to searching

* doc/lispref/searching.texi (Regexp Functions, Regexp Search):
(Simple Match Data, Saving Match Data, Standard Regexps): Copyedits.
(Regexp Functions): Mention regexp-opt is not guaranteed.
Mention regexp-opt-charset.
(Regexp Search): Recommend against looking-back.
(Search and Replace): Use Texinfo recommended quote convention.
Add more query-replace-map items.  List multi-query-replace-map items.

* lisp/replace.el (query-replace-map): Doc fix.

* admin/FOR-RELEASE: Related markup.