Giraffe: jsonChunked does not follow RFC

[TheAngryByrd]

The jsonChunked function does not follow the RFC for Transfer-Encoding: chunked.

jsonChunked calls SerializeToStreamAsync on the current JsonSerializer.

https://github.com/giraffe-fsharp/Giraffe/blob/6e33155d3f0929af52886a7302fbd12a07ff9cb7/src/Giraffe/ResponseWriters.fs#L156-L163

Which SerializeToStreamAsync's implementation is writing directly to the output stream

https://github.com/giraffe-fsharp/Giraffe/blob/7981279dfef1432b271975449c8fcb5935cf977c/src/Giraffe/Serialization.fs#L95-L99

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If you use curl to hit an endpoint using jsonChunked you'll get an error

* Illegal or missing hexadecimal sequence in chunked-encoding
* stopped the pause stream!
* Closing connection 0
curl: (56) Illegal or missing hexadecimal sequence in chunked-encoding

Similarly browsers and javascript libraries don't know how handle this response. The problem is it doesn't follow the RFC for Transfer-Encoding: chunked.

The RFC BNF is shown below

       Chunked-Body   = *chunk
                        last-chunk
                        trailer
                        CRLF

       chunk          = chunk-size [ chunk-extension ] CRLF
                        chunk-data CRLF
       chunk-size     = 1*HEX
       last-chunk     = 1*("0") [ chunk-extension ] CRLF

       chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
       chunk-ext-name = token
       chunk-ext-val  = token | quoted-string
       chunk-data     = chunk-size(OCTET)
       trailer        = *(entity-header CRLF)

An example of this is from MDN

HTTP/1.1 200 OK 
Content-Type: text/plain 
Transfer-Encoding: chunked

7\r\n
Mozilla\r\n 
9\r\n
Developer\r\n
7\r\n
Network\r\n
0\r\n 
\r\n

If we're going to keep the interface of writing to a Stream for the json serializer, we're going to have to implement some type of Stream that handles writing this format to the HttpContext's response stream.

[NinoFloris]

I'm going to close this on account of #369 being merged, if anything still needs to happen best to open a new issue!