Updates readme to be ready to make the repo public.
Fix for older versions of django -- we explicitly say this package only works with 1.7+, but who knows how and where this code could eventually get used -- compatibility is a good in its own right.
Fixes corner case in CssAbsolute:  (Using a Cached S3 storage AND the file to concatenate isn't available on the local filesystem) which happens when the results of collectstatic aren't available locally for the request.

The fallback system was working, files were being included individually, but concatenation wasn't happening reliably.

The corner case:
E.G. This happens on Heroku when `DISABLE_COLLECTSTATIC` is set.  When DISABLE_COLLECTSTATIC is set, the local cache results of collectstatic are put on a worker node which is destroyed at the end of the command and the collected files aren't added to the compressed application slug which will be used to spin up new dynos.

This manifestation on heroku is a specific case, the general case has the ability to arise anywhere the local filesystem is treated as ephemeral (especially if there are >1 servers).
A first cut at addressing #4.
merge conflict