RUBY-565 "advanced ssl" support for peer certificate validation

* added support for peer certificate and hostname validation
* cleanup and creation of test fixtures folder
* updated `MongoClient` and `MongoReplicaSetClient` docs
* minor update to yardoc template

Running these tests requires building MongoDB with SSL support (OpenSSL 1.0+).

Instructions on how to do so can be found here:
http://www.mongodb.org/about/tutorial/build-mongodb-on-os-x/
http://www.mongodb.org/about/tutorial/build-mongodb-on-linux/