Added properties for changing the diameter.
Added properties for changing the diameter.

weidnem/IntroPython2016,weidnem/IntroPython2016,UWPCE-PythonCert/IntroPython2016,weidnem/IntroPython2016,UWPCE-PythonCert/IntroPython2016,UWPCE-PythonCert/IntroPython2016