Support column function on Label

[Yancey0623]

Is your feature request related to a problem? Please describe.

For some cases, the label is not an integer feature instead of an one hot vector:

y_true = tf.reshape(
                tf.one_hot(features['item'], 200, on_value=1, off_value=None,
                           axis=1), [-1, 200])

The SQL can be like :

COLUMN ...
LABEL RESHAPE(ONE_HOT(label, 200), [-1, 200])

[tonyyang-svail]

Related #588