New visitor classes missing from previous commit.

Remove line printing debug info.

Add classes to print status of AST (use only for debugging!)

Remove all remaining NULL (undefined) datatypes from IL code.

Move is_datatype_valid/equal() to get_datatype_info_c

Fix bug related to support of SAFE datatypes.

Set datatype of il_intruction_c objects containing an ST operator.

Delete unused variables.

Use doubly linked connections for flow control graph (will be used later).

Remove deprecated search_expression_type_c

Deprecate use of search_expression_type_c (prepare for complete removal!).

Deprecate use of search_expression_type_c (prepare for complete removal!)

Deprecating use of search_expression_type_c, so it may later be deleted!

Merge

Add new get_datatype_info_c (preparing to remove search_expression_type_c)

Delete declaration of unused & undeclared functions.

Delete class elements that are not used (clean up code).

Add check whether external var matches to global var.

Also check FB passed as parameters in FB/Function calls (Thanks Andreas!)

Minor changes needed to build with pedantic flag.

Also check external/global variable consistency in configurations and FBs.

add method for printing class_name. USE ONLY FOR DEBUGING!

store POU reference to POU declaration instead of global var declarations.

Start declaration check class.