Improve validation of function names:
1. Relax checking to accept function types of the form
"ret_type (fname)(args)" (suggested by Yuri Pankov <yuripv dot net>).
2. Tighten checking to require the closing parenthesis.

Messages of the -Wbase level now print STYLE:. Since this
causes horrible churn anyway, profit of the opportunity to stop
excessive testing, such that this is hopefully the last instance
of such churn. Consistently use OpenBSD RCS tags, blank .Os,
blank fourth .TH argument, and Mdocdate like everywhere else.
Use -Ios=OpenBSD for platform-independent predictable output.

warn about parentheses in function names after .Fn and .Fo;
particularly useful when converting from other languages to mdoc(7);
feature suggested by bentley@

Messages of the -Wbase level now print STYLE:. Since this
causes horrible churn anyway, profit of the opportunity to stop
excessive testing, such that this is hopefully the last instance
of such churn. Consistently use OpenBSD RCS tags, blank .Os,
blank fourth .TH argument, and Mdocdate like everywhere else.
Use -Ios=OpenBSD for platform-independent predictable output.

warn about parentheses in function names after .Fn and .Fo;
particularly useful when converting from other languages to mdoc(7);
feature suggested by bentley@