Update copyright and leading comment.

Update copyright and leading comment.
(regexp-opt): Update comment and adapt the code the new meaning of the
`paren' argument of regex-opt-group for shy-groups.
(regexp-opt-depth): Handle shy groups as well as backslashed backslashes.
(regexp-opt-group): Turn the leading comment into a docstring.
Allow `paren' to be a string (the string to use to open a group).
Remove open-presuf and close-presuf.
Instead of checking for `all one-char' and then later on check for
`several one-char', handle both cases close together.
Also apply a more generic algorithm for suffixes (the mirror image
of the algorithm used for prefixes).
Use shy-groups.
\Use nreverse rather than reverse.
(regexp-opt-try-suffix): Removed.