TODO

* pointers to array elements and struct elements
* setjmp() / longjmp() hooks for error exit
* test character array pointers and dereferencing
* operator precedence
* '->'
* make printf() honour memory constraints
* interactive mode
* casts
* enum
* '+=' / '-=' for pointers
* pointer arithmetic
* change heap to use a single consistent freelist node struct
* periodic heap cleanup
* fix type comparison to take into account array size
* fix return of array types
* expression and auto-cast support for all types
* octal/hex character constants
* fix #include
* assignment on declaration

Need test/debug:
* all break/continue variations
* #define

Also:
* Remove Var parameter from HeapPopStack() once we're certain it all works