added support for us020 ultra sonic range finder

samples/us020.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"log"
+	"time"
+
+	"github.com/kid0m4n/go-rpi/sensor/us020"
+)
+
+func main() {
+	rangeFinder := us020.New(10, 9)
+
+	for {
+		distance, err := rangeFinder.Distance()
+		if err != nil {
+			log.Panic(err)
+		}
+		log.Printf("Distance is %v", distance)
+
+		time.Sleep(500 * time.Millisecond)
+	}
+}