Features

• Disable tree pruning in the CART algorithm if the validation dataset is empty (i.e. validation_ratio=0).
• Migration to Tensorflow 2.6. You will see an undefined symbol error if you install this version with a TensorFlow version different than 2.6. Previous versions were compiled for TF 2.5.

Fixes

• Fix failure from Github Issue #45 where the wrong field was accessed for leaf node distributions.
• Fix saving of categorical features specification in the Builder.