Support versions of rest-client < 1.7.0 such as 1.7.0.rc1 which check ssl certificates by default

As gem specification for restfully allows for rest-client v 1.7.0.rc1 to be pulled, restfully's behaviour will change when connecting to https servers with certificates that do no validate against system-wide certificate authorities. 

This commits add support for ssl options such as verify_ssl and any option name starting with ssl to be passed to be saved at session level and used by RestClient::Request when creating a RestClient::Resource

This might mean the restfully.gemspec could be updated to support rest-client in the 1.7.x branch