Disable constant propagation again (still not working correctly)

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.

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).

Delete un-used declaration.

merge

Allow variables to be used when declaring the dimension of an array.

Fix C code generation when forward references (-p command line option) is on.

Add a new pou_typename_c object to the AST to store references to previously declared Functions, FB, and Programs.

Delete unused file.

Make use of pre-parser a command line option.

Fix AST generated by parsing with preparsing switched OFF (typo in array datatypes, and fix parsing of POUs).

Fix AST generated by parsing with preparsing switched on, and allow parsing to work with preparsing off.

Fix bug introduced when adding support for relaxed datatype model: change derived_datatype_identifier_c to identifier_c when used as an identifier

Add a pre-parsing phase to stage1_2 (allows source code that references POUs and datatypes before they are declared)