Node placeholder API

ASDisplayNodes now have an overridable method -placeholderImage that lets you provide a custom UIImage to display while a node is displaying asynchronously. The default implementation of this method returns nil and thus does nothing. A provided example project also demonstrates using the placeholder API.
Ahhh, I misunderstood the inset then, thinking it was what's here now. Makes waaaayy more sense now.

I'm up for the challenge of adding line-based text placeholders in this release if you're game :wink: