Replaced subscribe.{h,c} by stripped-down async handling.
Replaced subscribe.{h,c} by stripped-down async handling.

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