Mobj Layers
Mobj layers are a new modding feature that allows you to change what layer each mobj is located at. This merge request adds the mo.layer field which expects a fixed_t value. Please note that by default, every mobj is at layer 0, which is the global layer. You can only collide with mobjs on all layers including the global layer if you are located at the global layer. Otherwise, if you are not in the global layer you will only be able to collide with mobjs that are the same layer that you are located in as well as the global layer.
