Update examples/etsi_iot_01.c to use the new API
Update examples/etsi_iot_01.c to use the new API

Update all the coap_ calls to use the new API, and the updated structures.
Introduce using session instead of context.
Correct all the compiler warnings.
Keep the payload in the resource rather than separately.

authmillenon/libcoap,authmillenon/libcoap,authmillenon/libcoap