Write "0\r\n\r\n" to the end of HTTP streams

HTTP Streams must be terminated by an empty chunk, or certain clients
will raise errors. For example, trying to `curl` a streaming endpoint
will finish with:

`curl: (18) transfer closed with outstanding read data remaining`

Ensure that streaming endpoints write an empty chunk, denoted by
"0\r\n\r\n" before closing.

Signed-off-by: David Celis <me@davidcel.is>