Improve ssl settings accoring to Mozilla's SSL recommendations here:
https://wiki.mozilla.org/Security/Server_Side_TLS#Nginx

Site now scores an A on qualys ssl test:
https://www.ssllabs.com/ssltest/analyze.html?d=pencilcode.net

Note that https on the site is not compatible IE6-IE8 on XP, due
to deprecating old cipher suites.