Tidy up the general proxy logic by moving common functionality
into libcoap.
New functions coap_proxy_forward_request(), coap_proxy_forward_response()
and coap_proxy_is_supported() added.
New --enable-proxy-code support added to configure.
New ENABLE_PROXY_CODE support added to CMakeLists.txt.
Support for common shared connection to next hop.
Support for round-robin balancing across multiple next hops.
Optional compile time thread safe code supported.
Locking is done at the coap_context_t level, and if enabled is primarily
done coap_threadsafe.c and coap_threadsafe_internal.h.
coap_threadsafe_internal.h causes coap_X() to get mapped to coap_X_locked()
throughout the libcoap library code with the exception of coap_threadsafe.c
if thread safe is enabled.
Jon Shallow