moved class phpdoc below the namespace definition, cleaned up white-
space in a comment
removed redundant constant (has been moved to Client)
factored out some stuff to a base request class
renamed performRequest() to sendRequest()
factored out creation of the Zend\Http\Request object to a separate
method
improve comments a bit
added sendNotification() method for sending notification requests to
the server
moved request classes under a separate namespace