Dirty object-based approach

Contrasting with #3, this approach is more efficient as it requires only a single call to add/update/delete metadata for a single container.

The dirty object idiom diverges from the existing idioms.  However, Looking at the API docs for CloudFiles objects, I suspect that a similar idiom will be desirable for Object metadata and perhaps content as well.
I'm trying to remember what Ruby version introduced `#each_with_object`. Was it 1.9.x?