add observe to example server
add observe to example server

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