Make stream reading from STDIN available

[ecklm]

This enhancement would enable the user to make accessible any file-based data generated on the fly without storing it.

It might be useful for serving any type of compressied content or anything like this.

E.g. tar -xOzf foo.tgz bigfile | FileHTTPServer.py --from-stdin --filename "streamingly compressed file"

Of course it might be served only one time, but sometimes is a useful feature.