nanocoap: add coap_get_token()
nanocoap: add coap_get_token()

jasonatran/RIOT,OlegHahm/RIOT,miri64/RIOT,ant9000/RIOT,kYc0o/RIOT,kYc0o/RIOT,ant9000/RIOT,ant9000/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,kaspar030/RIOT,miri64/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,jasonatran/RIOT,miri64/RIOT,OlegHahm/RIOT,miri64/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kaspar030/RIOT,kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,kYc0o/RIOT,miri64/RIOT,kYc0o/RIOT