- Implement newInstance() for lang.Type and all its subclasses:
  . lang.XPClass - the value type
  . lang.Primitive - string, int, double, bool
  . lang.ArrayType - *[]
  . lang.MapType - [:*]
- Implement default for lang.Type and all its subclasses:
  . lang.XPClass - NULL
  . lang.Primitive - string "", int 0, double 0.0, bool FALSE
  . lang.ArrayType - []
  . lang.MapType - [:]
- Implement casting for lang.Type and all its subclasses