In HttpClient, add support for servers that do not send a Content-Type header.
Remove the need to wrap messages to send in a vector.
When writing a HTTP response, write the headers and body separately to prepare for chunked encoding.
Add streaming support to the HttpServer. A handler can now not only set a body in its Response but also a bodyChunkFunction(), which can supply the body chunk by chunk and finally throw a NoChunksLeftException. Chunks provided will be sent immediately.