Storing temporary request body on disk

Hi, I'm an Android application developer and interested in your project (NanoHTTPD.)

This patch allows it a) to write request bodies on disk not in memory,  and b) to clean up temporary files after each request served.

Certainly it hurts the server's performance for small requests, but it allows processing large request on memory-constrained platforms, such as Androids.

Would you please kindly review it?  Thank you.

Big hands from Japan,
Takahiro Yoshimura (@alterakey)