TODO

* struct
* pointers
* switch
* arrays
* operator precedence
* enum
* interactive mode

New type system:
* basic types: picoc int, picoc char, native int, native char
* structs
* arrays of picoc types or structs
* pointers to: 


Also:
* Change function store system to use dynamic allocation
* Check for Alloc returns checking NULL
* Do we really need OnHeap? Isn't every value on the stack anyway?
* Remove Var parameter from HeapPopStack() once we're certain it all works