Exit non-zero if find-doc-nits finds nits

Exit non-zero if find-doc-nits finds nits

Filter all output to a new &err() routine, which sets the global
exit status, $status.
Also, fix all subroutine definitions and references to be consistent:
no prototypes, no & before function calls.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Paul Yang <kaishen.yy@antfin.com>
(Merged from https://github.com/openssl/openssl/pull/9733)