Code cleanup: with the introduction of anotation_map[], generate_c_vardecl_c can now derive directly from generate_c_base_c

Fix typos in comments

Add comments, and make get_datatype_id_str_c equivalent to get_datatype_id_c

Fix calling of functions whose parameters are of an implicitly declared datatype (currently only makes sense for REF_TO datatypes, but may make sense to other datatypes too if the datatype model is changed in the future).