add libressl support
Created by: aduskett
Because LibreSSL returns 2.x for the version numbers, the macros think that OpenSSL 1.1 should be used. This patch checks to see if there is an LIBRESSL_VERSION_NUMBER defined.
Also, remove #include <openssl/cms.h> from include/sslapi.h. LibreSSL doesn't include it, and it's not required to compile against OpenSSL.
Thank you for such a great piece of software! Adam