`define` and `token` categories

[andreasabel]

This hasn't been tested with #266:

CNil.     Chars ::=                 ;
cSg.      Chars ::= Char            ;
CSnoc.    Chars ::= Chars Dot Char  ;

define    cSg c = CSnoc CNil (Dot ".") c;

token     Dot '.'                   ;

Affects:

• Haskell/Functor: fixed by 9db83ac
• Agda, because of --text-token: fixed by 2fc8d84
• C