Prevent shadow warnings
Also draw associations to specializations and generalizations of roots

Otherwise, if these concepts don't have attributes of their own, the associations to them will be left out.
Use --test for interface documentation
First version of documentation for messages

(Add "CLASS Message" after an interface name to classify it as a message interface) @stefjoosten: expression and definition will probably not both fit in the table, so we have to make a choice or think of some other presentation.
Only create messages chapter if there are message interfaces
Show interface name in message table in bold