packets, contiguous memory, and buffer chains

[guruofquality]

There are a few cases that come up where we end up copying buffers to form a contiguous buffer for a packet message:

• Consider the label deframer which might concatenate several buffers to form a complete packet.
• Consider a protocol framer which appends a protocol header with a payload buffer.

It might be desirable to have a chain of buffers constitute a packet and to pass this chain around instead. This would allow the consumer to decide that it must copy them into contiguous memory to perform useful work. In some cases, the buffers can just be forwarded, truncated, and sliced up as-is and we want to enable this possibility.

This basic concept already applies to the stream domain, it would be nice to bring it over to the packet domain and allow for the two to interchange fairly easily. We might create a BufferChain object which is basically a vector/list/queue of BufferChunks with some convenience routines for removal, pushing to a stream, overall length, appending...

[guruofquality]

This issue was moved to pothosware/PothosCore#62