Move address resolution out of core and into app
Move packet transmission out of core and into application
Fix int64_t use in printf
Fully remove networking I/O from core.
A network connection is now identified by three things
    int socket, an identifier for the transport, never dereferenced
    uint8_t *addr + size_t addrLen, an opaque buffer used by the the application to identify a destination

Socket transmit and receive code now lives purely in the application, with a callback being made when the core wishes to send data (see lwm2m_init()).

The current client and server apps are largely unchanged.
Future applications should be able to use the core without a BSD sockets interface.