Text macro processing

Similarly to the Conditional Evaluation, the text macro processing happens also at reading the timetable file, it operates also on the timetable file(s) as plain text.

The text macro processing is mostly an instrument to save typing work, but a few variables makes it possible t adapt the timetable file to some system parameters.

Commands of the text macro processing
%DEF, %DEFINE, %DEFMAC Define a text macro, obeying macro processing during the definition of the macro body
%*DEF, %*DEFINE, %*DEFMAC Define a text macro literally (do not run macro processing, while defining the macro body)
%LEX, %LIBEX, %LIBRARYEXISTS Check, if a picture library is available.
%FEX, %FILEX, %FILEEXISTS Check, if a file (either image file, picture library or timetable file) is available.
%PEX, %PICEX, %PICTUREEXISTS Checks, if a picture with the given name is available in the stock list.
%EVAL Evaluate an arithmetic/logic expression, and deliver the result as a number