parsers.
This consists of two parts:
1. The generated Flow classes expose their flow buffers via a new
method flow_buffer().
2. Flow buffers get two new methods:
// Interface for delayed parsing. Sometimes BinPAC doesn't get the
// buffering right and then one can use these to feed parts
// individually and assemble them internally. After calling
// FinishBuffer(), one can send the uppper-layer flow an FlowEOF()
// to trigger parsing.
void BufferData(const_byteptr data, const_byteptr end);
void FinishBuffer();
