Ability to control SSL settings of underlying Net::HTTP

Changes:
* Allow SSL attributes to be set on underlying Net::HTTP instance. Namely ca_file and ca_path.
* Set verify_mode to OpenSSL::SSL::VERIFY_PEER. That is the default in 1.9 but in 1.8.7 its VERIFY_NONE.
* Added tests for setting ssl attributes and http headers. Brought in rspec and fakeweb to help with that.