Minor Description
Adding Specificity metric (= true negative rate) to MulticlassMetrics.scala
1. Add specificity calculations:
pecificity (SPC) or true negative rate
SPC = TN / N = TN / (TN+FP)
False Positive Rate (FPR)
FPR = FP / N = FP / (FP + TN) = 1-SPC
SPC = 1 - FPR
2. Add specificity tests to :
mllib/src/test/scala/org/apache/spark/mllib/evaluation/MulticlassMetricsSuite.scala
