Added ELNode.DeleteKey, * and % operators
Added support for loading files in global KB

Make a KB component in an object called “Global” and its KnowledgeBase
will be the actual Global KnowledgeBase.
Prolog goal stack now tracks current rule

So it can print what line it’s on.  Also, somewhat rationalized the
goal stack.
Rationalized code for PrologContext

Goal stack now has most of the data in a single array of structs rather
than parallel arrays.

Also rationalized some of the layout of the code and added some
comments.
Marginally improved collision avoidance

But it still really needs to be rewritten from the ground up.