Add support for chunked requests

This patch adds support for dealing with chunked POST and PUT requests. A chunked body contains sets of chunks as follows:

<length of 1. chunk in hex>'\r\n'
<chunk data>'\r\n'
<length of 2. chunk in hex>'\r\n'
<chunk data>'\r\n'
...
<length of n. chunk in hex>'\r\n'
<chunk data>'\r\n'
'0\r\n'
'\r\n'