Move the Date struct into types and implement a get_property_numeric.

src/parser/org_source.rs

@@ -388,6 +388,7 @@ impl<'s> From<CustomError<OrgSource<'s>>> for CustomError<&'s str> {
             CustomError::MyError(err) => CustomError::MyError(err.into()),
             CustomError::Nom(input, error_kind) => CustomError::Nom(input.into(), error_kind),
             CustomError::IO(err) => CustomError::IO(err),
+            CustomError::BoxedError(err) => CustomError::BoxedError(err),
         }
     }
 }