util/find-doc-nits: more precise option and function name checker

util/find-doc-nits: more precise option and function name checker

The checks for our uses of 'B<' and 'I<' for options, and possibly
function names, was over-reaching quite a bit.

So we fine-tune it a bit:

- by only checking for options in man1 pages, and only in SYNOPSIS
  and *OPTIONS sections.
- by only checking for function names in man3 pages.

The man1 option checker has the additional check that options found in
*OPTIONS are also found in SYNOPSIS andd vice versa.

In all cases, this also handles options and function names with
additional markup, such as 'B<-I<cipher>>' and 'B<sk_I<TYPE>_push>'.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10073)