Add comments.

Add checks for use of non constant value in subranges, and lower_limit > upper_limit.

Fix previous commit (symtable operator[] must return a reference to the stored value!)

Do constant propagation of configuration/resource variables, taking into account scope of variables.

Change dsymbtable_c -> use design pattern used by C++ standard library (STL)

Change symbtable_c -> use design pattern used by C++ standard library (STL)

Remove debugging code left in by mistake.

Do constant propagation inside Configurations and Resources (required for support of extension: array [1..max] OF int); (Resources is still buggy)

Do constant folding of default initial values of datatypes.

Do constant propagation to symbolic_variables, and correctly handle constant folding and propagation of variable declarations.

When generating C code, use the const_value of a symbolic_variable when it is used in a subrange.

Small code re-organization of how const values are stored in symbol_c (can now be accessed through member functions, instead of macros)

Fix bugs introduced in previous commit (once again do constant folding of all literals in type declarations)

Do constant folding of variable's initial value (allows correct C code generation with variables in the subrange of an array declaration: ARRAY [1..max] of INT).