mfc class and self not supported

```
function get_tmask(self) result(tmask)
  implicit none
  class (grid_type), target, intent(in) :: self
  integer, pointer :: tmask(:,:)
  tmask => self%tmask
  return
end function get_tmask
```
```
grid_mod.f90:3:3: error: sorry: CLASS type-specifier not implemented
grid_mod.f90:5:12: error: entity 'self' does not have any IMPLICIT type
```

```