Improve docs and developer experience for working with the adaptive resolution system

[Keavon]

• Improve developer experience for writing nodes which take adaptive resolution data (like Copy to Points) - a way of generalising and automating manual composition - automatic copying of the primary input to parameters (always do that and discard if unused? essentially acts as the automatic insertion of cull nodes?)
• More docs for the macros like node_fn (and the confusing similar ones to that)