Setting Content-Encoding on Cloudfiles upload

There doesn't appear to be any way to set `Content-Encoding: gzip` on uploaded files.  In python-cloudfiles you can manually set headers on the storage object you get by calling `container.create_object()` before you call `send()` on it.

See http://docs.rackspace.com/files/api/v1/cf-devguide/content/Enabling_File_Compression_with_the_Content-Encoding_Header-d1e2198.html