remove ginext/mongoext (no-dep lib)

mathext/math.go

@@ -0,0 +1,13 @@
+package mathext
+
+func AvgFloat64(arr []float64) float64 {
+	return SumFloat64(arr) / float64(len(arr))
+}
+
+func SumFloat64(arr []float64) float64 {
+	sum := 0.0
+	for _, v := range arr {
+		sum += v
+	}
+	return sum
+}