added option -f for sending payload
added option -f for sending payload

nmacs/libcoap,pabigot/libcoap,fredericgermain/libcoap,sgso/libcoap,joaopedrotaveira/libcoap,pabigot/libcoap,joaopedrotaveira/libcoap,sgso/libcoap,gebart/libcoap,markushx/libcoap,PolymorhicCode/libcoap,gebart/libcoap,nmacs/libcoap,pabigot/libcoap,thecodemaiden/libcoap-fork,OlegHahm/libcoap,alexaring/libcoap,thecodemaiden/libcoap-fork,authmillenon/libcoap,markushx/libcoap,alexaring/libcoap,authmillenon/libcoap,gebart/libcoap,joaopedrotaveira/libcoap,RIOT-OS/libcoap,authmillenon/libcoap,fredericgermain/libcoap,sgso/libcoap,alexaring/libcoap,nmacs/libcoap,markushx/libcoap,OlegHahm/libcoap,RIOT-OS/libcoap,OlegHahm/libcoap,fredericgermain/libcoap