Closures for dynamic response handling.

  Instead of having different methods that handle the response
  differently, we are opting for simply passing a block to the request
  method. This makes response handling very modular. The two currently
  defined are &instantiate_object and &update_self--response handling
  blocks are defined in PS::Object. &instantiate_object returns an array
  of instantiated subclasses of PS::Object. &update_self updates the
  current object's attributes with that of the results. Response blocks
  are passed to request.

  Change PS::Psobject's name to PS::Object--it was named Psobject due to
  fear of overwriting the object class in ruby. Moved subclasses of
  PS::object under an objects directory.

  Added simplecov and got the coverage of the core classes to 100% with
  the subclasses of PS::Object to 80.73%.