Added driver for BH1750 digital ambient light sensor (#15)

* Added driver for BH1750 digital ambient light sensor

examples/bh1750/main.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"time"
+
+	"machine"
+
+	"github.com/tinygo-org/drivers/bh1750"
+)
+
+func main() {
+	machine.I2C0.Configure(machine.I2CConfig{})
+	sensor := bh1750.New(machine.I2C0)
+	sensor.Configure()
+
+	for {
+		lux := sensor.Illuminance()
+		println("Illuminance:", lux, "lx")
+
+		time.Sleep(500 * time.Millisecond)
+	}
+}