Where to extract the key and value from a line is specified by `key_index` and
`value_index`.

- A value of -1 means use the line number(starting from zero), expects `int64`.
- A value of -2 means use the whole line content, expects `string`.
- A value >= 0 means use the index (starting at zero) of the split line based
  on `delimiter`.
  }];

  let arguments = (ins

*   Added a `model.export(filepath)` API to create a lightweight SavedModel artifact that can be used for inference (e.g. with TF-Serving).