added simple example demonstrating user-defined timeout function
added simple example demonstrating user-defined timeout function

arurke/contiki,MohamedSeliem/contiki,arurke/contiki,bluerover/6lbr,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,bluerover/6lbr,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,arurke/contiki,bluerover/6lbr,MohamedSeliem/contiki,MohamedSeliem/contiki