Align documentation with reality

OK tb@

Add a roff comment saying that X509_name_cmp(3) is intentionally
undocumented because it is almost unused in real-world code.
OK tb@

add a comment saying that name_cmp() is intentionally undocumented;
tb@ agrees that it should not be part of the public API

New manual page X509_cmp(3) documenting the same public functions
as in OpenSSL 1.1.1. I rewrote most of the text for clarity, precision,
and conciseness and added some additional information. A fe

New manual page X509_cmp(3) documenting the same public functions
as in OpenSSL 1.1.1. I rewrote most of the text for clarity, precision,
and conciseness and added some additional information. A few sentences
from Paul Yang remain.

show more ...