Add support for nested comments

Fix bug: when checking compatibility between GLOBAL and EXTERNAL variables, must only enforce GLOBAL CONSTANT => EXTERNAL CONSTANT.
Reverse CONSTANT implication is not enforced, and neither is RETAIN compatibility.

merge

Fix bug: correctly generate code when accessing external variables declared inside FBs as a structured variable (realvar := fb1.fb2.extvar1.realvar)

Fix bug in standard: standard does not allow multiple VAR_GLOBAL ... END_VAR constructs in configurations and resources. This is probably a bug, so we allow it.

Code cleanup (part 3): generate_c_typedecl_c is no longer needed for code generation in POUS.c It is now only needed for datatype declaration in POUS.h

Code cleanup (part 2): generate_typedecl_c now only prints to POUS.h !

Code cleanup (part 1): subrange check functions are now declared in POUS.h (as static inline functions or #define)

Fix get_datatype_info_c::is_subrange(), which did not work when using base type! (we now use get_equivtype() instead of get_base_type() )

fix a couple of typos.

Fix bug - correctly declare struct members whose type is a directly defined array (e.g.: STRUCT x: ARRAY of XXX; END_STRUCT)

Start using the called_fb_declaration annotation when generating C code from FB calls in ST.