Make support for use of variables in array size declarations a command line option (off by default)

Add debug_c::print(const_value_c) for printing of const values.

Add is_undefined() method to const_value_c

Make error message more informative.

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.