Fixing issue where ASaP::getReturnType did not properly update the InheritanceMap pointer
of the returned type. To do that, we needed access to the SymbolTable. So I made the
symbol table a singleton object (constructor & destructor are private, called by the
Initialize and Destroy static functions to build and tear down the class static variable
Table, which is accessible by all the code). I will need to clean up the rest of the
code to remove unnecessary passing of references to the now singleton Symbol Table).