Feature Suggestion: support stream

[beenotung]

It would be more efficient if smart-buffer can be used around readable stream and writeable stream.

A potential use case is to append a stream of objects encoded by msgpack (write the length, then write the buffer for each object). The stream can be written to a file or socket.
Then the other side can decode the stream of length and buffer (then decoded into object by msgpack).

Currently, smart-buffer only support decoding from a buffer, which require the complete binary data to be read from the disk or received from the socket.