Simplify EnumDataType and Instance specification

Currently EnumDataType instances need to be specified with explicit DataTypes, e.g.:

  Enumerated e1 {
  	e1 v1, 
  	e1 v2 
  }

where v1 and v2 are the instances of the EnumDataType. This can be tedious. It should be possible to infer the data types for the instances from the containing EnumDataType so that it is also possible to only list the instances, e.g.:

  Enumerated e1 {
  	v1, 
  	v2 
  }