Append to set

#1327 needs an associated PR to bring collection/composite views in sync with it.

This one uses the verb `attach`, which I actually prefer over `set`. The reason why is because of the buffer methods. Because of this I think we should rewrite history for #1327 to be `attachHtml` instead of `setHtml`. @samccone I think this should be fine for Bower as we're only modifying history **after** the latest tag.