http: support chunked transfer-encoding

[legendecas]

By default, http module cannot not automatically derive content-length from input data since ClientRequest is a duplex stream, client can continuously write data into stream if the stream is not ended, yet headers have been sent at the beginning of the request.
Thus the http client in node.js set header Transfer-Encoding with chunked by default, then encase data with an chunk length at the beginning of each chunk.

[yorkie]

This has been fixed at #174.