renamed direction to side

internal/side.go

@@ -0,0 +1,28 @@
+package internal
+
+type Side uint
+
+const (
+	SideUnknown Side = iota
+	SideBuy
+	SideSell
+)
+
+func (d Side) String() string {
+	switch d {
+	case SideBuy:
+		return "buy"
+	case SideSell:
+		return "sell"
+	default:
+		return "unknown"
+	}
+}
+
+func (d Side) IsBuy() bool {
+	return d == SideBuy
+}
+
+func (d Side) IsSell() bool {
+	return d == SideSell
+}