Tracking Objects

Our virtual machine needs to track every Snek object that gets created.

We are no longer going to track how many times an object is referenced, but instead check at garbage collection time if each object is still referenced at all. If it is, keep it. If not, free it.

Assignment

1. In vm.c complete the vm_track_object, which adds an object to our vm->objects stack in a more type-safe way.
2. In sneknew.c update the _new_snek_object function. Before returning the newly allocated object, it should ensure it's tracked by the VM.