Cross section levels

Currently, rendered levels don't expose what's below it, so a lot of photoshop work is necessary to get levels to work correctly on many maps in a VTT. E.G., a colliseum like level with tall areas around a central depression doesn't work correctly.

Ideally this functions like a slicer, allowing you to render across a level with transparency, and would optimally include a solution for things like tree trunks for characters standing under a tree so that the token doesn't render over the static treetop.