Unit testing for def/ module.

Added unit tests to test code in def/ module.

vendor/github.com/montanaflynn/stats/softmax.go

@@ -0,0 +1,25 @@
+package stats
+
+import "math"
+
+// SoftMax returns the input values in the range of 0 to 1
+// with sum of all the probabilities being equal to one. It
+// is commonly used in machine learning neural networks.
+func SoftMax(input Float64Data) ([]float64, error) {
+	if input.Len() == 0 {
+		return Float64Data{}, EmptyInput
+	}
+
+	s := 0.0
+	c, _ := Max(input)
+	for _, e := range input {
+		s += math.Exp(e - c)
+	}
+
+	sm := make([]float64, len(input))
+	for i, v := range input {
+		sm[i] = math.Exp(v-c) / s
+	}
+
+	return sm, nil
+}