Add support for generating DANE TLSA records to genssl.

This is based on the information provided at http://ahf.me/articles/2013/09/14/enhancing-ssl-security-for-irc-dane-support/. I can sadly not test this due to my domain registrar not supporting DNSSEC/TLSA but it should be correct according to this post. If anyone else has a domain registrar who can test this it would be appreciated if you could.