Various small changes in addition to the following.

Various small changes in addition to the following.
(Regexp Example): Adapt to new value of `sentence-end'.
(Regexp Functions): The PAREN argument to `regexp-opt' can be `words'.
(Search and Replace): Add usage note for `perform-replace'.
(Entire Match Data): Mention INTEGERS and REUSE arguments to `match-data'.
(Standard Regexps): Update for new values of `paragraph-start' and
`sentence-end'.