Enclose following ARG sexps in parentheses.
Leave point after open-paren.
A negative ARG encloses the preceding ARG sexps instead.
No argument is equivalent to zero: just insert `()' and leave point between.
If `parens-require-spaces' is non-nil, this command also inserts a space
before and after, depending on the surrounding characters.
If region is active, insert enclosing characters at region boundaries.
This command assumes point is not in a string or comment.