In pursuit of the idea that all CSS tasks should be handled by More, cache breaking of referred to resources should be added.
At a minimum:
For both usages, references that can be resolved (sprites, @imports if the file exists, url(), and so on) should have stable cache breakers to minimizes unnecessary re-downloads. In other cases, the hash should be monotonically increasing to avoid mishap.
Very basic attempt at #13, adding automatic cache breakers
Upon further reflection, the built-in function requires more string manipulation than I'd be comfortable promoting.
More should be purely declarative, that'd be veering a little too close to proper computation.