added docs and tests

      if True, the best model is considered to be the one that minimizes the

      validation metric.  If False, the best model is considered to be the one

      that maximizes it.

    transformers: List[Transformer]

      List of `dc.trans.Transformer` objects. These transformations

      must have been applied to `dataset` previously. The dataset will

      be untransformed for metric evaluation.

    """

    self.dataset = dataset

    self.interval = interval

import tempfile

import deepchem as dc

import numpy as np

import tensorflow as tf

try:

  from StringIO import StringIO

except ImportError:

        30, [metric],

        log,

        save_dir=save_dir,

        save_on_minimum=False)

        save_on_minimum=False,

        transformers=transformers)

    model.fit(train_dataset, callbacks=callback)

    # Parse the log to pull out the AUC scores.