This has the benefit that we don't need to duplicate the data at
different places.
* src/autofit/afwrtsys.h: New file.
* src/autofit/aftypes.h (AF_WritingSystem): Include `afwrtsys.h' to
define the enumeration values.
* src/autofit/afglobal.c: Include `afwrtsys.h' to get the writing
system specific header files.
Include `afpic.h'.
(af_writing_system_classes): Include `afwrtsys.h' to fill this
array.
* src/autofit/afpic.c: Include `afwrtsys.h' to get the writing
system specific header files.
(autofit_module_class_pic_init): Include `afwrtsys.h' for
initialization.
* src/autofit/afpic.h (AF_WRITING_SYSTEM_CLASSES_COUNT,
AF_WRITING_SYSTEM_CLASSES_REC_COUNT): Removed. Use
`AF_WRITING_SYSTEM_MAX' instead.