Set up a coap_io_process() loop spread across multiple threads, each thread
repeatably calling coap_io_process() and so able to handle any input packets.
Note that the application handlers need to be thread-safe for application
level activity.
Add 2 new main functions
coap_io_process_loop()
coap_io_process_terminate_loop()
Add in 2 new sub functions
coap_io_process_configure_threads()
coap_io_process_remove_threads()
to set up the parallel threads.
Update example servers to include using coap_io_process_loop().
Support optional thread number logging by configuration to maintain
backwards logging format output if required.
Jon Shallow
cce7b65398