This creates a separate events interface structure
for CurlResponderBuffer (AICurlResponderBufferEvents)
for dealing with received HTTP headers.
The headers are passed to the Responder, but only
if the class derived from Responder implements
completedHeaders (otherwise it makes little sense
to even decode the headers).
Basically this is a reimplementation of the functionality
of the old LLHTTPClientURLAdaptor class.
