Add "confidence" parameter to `metrics.probability_of_false_alarm`

[jarq6c]

Confidence (C) is 1 - FAR. This can be accomplished with a simple parameter and a partial function.

To completely duplicate the reference below, metrics will also need a way to accommodate "near misses" and "near hits" given some tolerance.

Should also consider adding convenience methods called false_alarm_ratio and false_alarm_rate.

Wells, S., Robson, A., Moore, R. J., Cole, S. J., & Rudd, A. (2016). Understanding the national performance of flood forecasting models to guide incident management and investment. In E3S Web of Conferences (Vol. 7, p. 18007). EDP Sciences.