Change referenced item list policy

Now in 1D, referenced face and edge lists are defined according to referenced node lists. And in 2D, referenced edge lists are defined according to referenced face lists.

Note that lists are duplicated. This could be improved (sharing lists) but it would require (significant?) changes. Since the extra memory cost only occurs in 1D and 2D, it does not seem necessary.

src/language/PEGGrammar.hpp

@@ -46,7 +46,7 @@ struct real
                      >,
                 opt< exponent >
                 >,
-           seq< plus< digit, exponent > >
+           seq< plus< digit > , exponent >
          >{};
 
 struct escaped_c : one< '\'', '"', '?', '\\', 'a', 'b', 'f', 'n', 'r', 't', 'v' > {};