TCP support

[philcaonz]

Any thoughts about supporting TCP framing described in rfc8323?

A challenge I feel from my experience of this library so far is that CoAP_onNewPacketHandler expects an entire CoAP message, whereas a TCP being a stream, it may be needed to call CoAP_onNewPacketHandler multiple times to incrementally process a message.

[niondir]

My first thought is to add another layer that just converts the stream into a "message" which should be possible by parsing only a subset of the message structure. Then you can pass that message down to CoAP_onNewPacketHandler.