Fix various doc nits.

find-doc-nits warns if you don't give a "what to do flag"
Don't use regexps for section names, just strings:  More consistency.
Rename "COMMAND OPTIONS" to OPTIONS.
Fix a couple of other nit-level things.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2076)