Add support for implicitly declared REF_TO datatypes.

With -Op option --> Place implicitly defined datatypes in the .h file corresponding to the POU where they are used.

Add name of POU as prefix to names of implicitly defined datatypes

Implicitly defined array datatypes use new naming method (greatly simplifies stage 4 code).

array_specification_c may be used as a datatype! Add it to spec_init_separator_c

Change REF() operator to return the correct REF_TO datatype datatype.

Narrow array subscripts correctly, even in the presence of other datatype errors (so we do not generate error messages for array subscripts that do not contain errors).

Add support for REF_TO derived datatypes (along with datatype verification)

Add option to place each POU in a distinct .c and .h file pair.

code re-organisation. Preparing for the changes to come in the next commit (one C file for each POU)

Remove un-used parameter from class constructor.

Move standard FBs to a pre-converted C file, insted of converting them every time along with the IEC source.

Move library files compiled to C to their own subdiectory.

Fix stupid mistake in previous commit (use 'long double' instead of 'ld' in istandard library macro)

merge

Update build/compile instructions to reflect the fact that autoconf needs to be executed.