class_accuracy: Class accuracy
In mtfairbanks/graingr: Helper functions for Chicagoans

'class_accuracy()' provides common classification metrics to convey results business users will understand.

1	class_accuracy(df, truth, pred, pos_flag = 1)

`df`	tibble A data frame containing the truth and prediction columns
`truth`	factor A column identifier for the true class results (that is a factor). This should be an unquoted column name.
`pred`	factor A column identifier for the predicted class results (that is also a factor). This should be an unquoted column name.
`pos_flag`	numeric/factor A numeric or string indicating the "positive" class.