New illustrations

* change feeds
   * http://192.168.0.159:8888/docs/changefeeds
* dates and times
    * http://192.168.0.159:8888/docs/dates-and-times
* sql to reql cheatsheet
    * http://192.168.0.159:8888/docs/sql-to-reql
* securing your cluster
    * http://192.168.0.159:8888/docs/security

Also added the table-joins image to the eq_join api page
    * http://192.168.0.159:8888/api/python/eq_join
    * http://192.168.0.159:8888/api/javascript/eq_join
    * http://192.168.0.159:8888/api/ruby/eq_join

\cc @ahruygt @mglukhovsky