Ancona xsendfile

This pull request brings in a reverted change for the experimental C::Utils::filehandle_response_at_path, which was discussed and turned out to be a bad idea, and the documentation patch.

If you want just to cherry-pick 5385778cb70ef0024d6cd3e4a876bfba46fa3ed3 or merge the whole branch is up to you.

Best wishes.