Tapot

Results 5 issues of Tapot

Main changes: - add DataIntegrityNullValuesMetrics metric - add test TestNumberOfDifferentNulls - add test TestNumberOfNullValues Aux: - some small style fixes

Add a method for test generation for all columns/nums features only/cat features only/features only cases Usage examples are in added notebook

If a category feature has mixed string and int-like values, DataDrift report raises an error `TypeError: '

- add ColumnDrift implementation

If we have more than 1000 values in a reference dataset and NaN values in a current dataset and try to get DataDrift report, an error `ZeroDivisionError: division by zero`...