indicator: add multiply operator

pkg/indicator/v2_multiply.go

@@ -0,0 +1,19 @@
+package indicator
+
+type MultiplyStream struct {
+	Float64Series
+	multiplier float64
+}
+
+func Multiply(source Float64Source, multiplier float64) *MultiplyStream {
+	s := &MultiplyStream{
+		Float64Series: NewFloat64Series(),
+		multiplier:    multiplier,
+	}
+	s.Bind(source, s)
+	return s
+}
+
+func (s *MultiplyStream) Calculate(v float64) float64 {
+	return v * s.multiplier
+}