Create Coverage.java

[gforman44]

Description

For regression problems, you'd like to know how often you're over-estimating the target. Sometimes you want to overestimate, say, 75% of the time, e.g. to make sure you have enough milk in stock to satisfy your customers.

• Note that this code could be generalized to reshape the predictions to match the labels. It re-uses the AbstractAccuracy class, which requires an axis number in its constructor, but this is ignored here, and generally for regression problems that don't use 1-hot encoding.