Support multiple adjustments on the same model instance with {% adjust_bulk %}

[melinath]

Right now, {% adjust_bulk %} lets you do an optimized adjustment of a bunch of (say) image fields for a queryset. But you can only do one adjustment per item in the iterable. That's a problem; often you'll have two fields that need to be adjusted, or one field that needs to be adjusted in two different ways. We should support that.

[melinath]

Specifically the issue here is that you might be looping over one iterable but want to have multiple images rendered for each item in the iterable - say, different sizes depending on window size or device resolution.