implement streaming requests

From what I can tell, chunked requests are indeed allowed and are commonly used by [phones](http://stackoverflow.com/questions/9543338/how-to-read-chunked-data-from-phone-gap-file-upload-in-android).

Nginx added [support](http://nginx.org/en/CHANGES) in version 1.3.9:
```
Changes with nginx 1.3.9                                         27 Nov 2012

    *) Feature: support for chunked transfer encoding while reading client
       request body.
...
```