Add OPENSSL_VERSION_AT_LEAST

added macro to create version number
use the macro to build OPENSSL_VERSION_AT_LEAST(maj,min,fix) so that
customers of libssl (such as ruby-openssl) do not need to be so aware of
openssl version numbers.
includes updates to ssl(7) and OPENSSL_VERSION_NUMBER(3) man page

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5212)