Support for DS1307 (#58)

* Support for DS1307

examples/ds1307/sram/main.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"machine"
+
+	"github.com/tinygo-org/drivers/ds1307"
+)
+
+func main() {
+	machine.I2C0.Configure(machine.I2CConfig{})
+	rtc := ds1307.New(machine.I2C0)
+	read := make([]byte, 5)
+	for {
+		rtc.Seek(0, 0)
+		_, err := rtc.Write([]byte{1, 2, 3, 4, 5})
+		if err != nil {
+			println("Error while writing data:", err)
+			break
+		}
+		rtc.Seek(0, 0)
+		_, err = rtc.Read(read)
+		if err != nil {
+			println("Error while reading data:", err)
+			break
+		}
+		for data := range read {
+			println(data, " ")
+		}
+
+	}
+
+}

examples/ds1307/time/main.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"machine"
+	"time"
+
+	"github.com/tinygo-org/drivers/ds1307"
+)
+
+func main() {
+	machine.I2C0.Configure(machine.I2CConfig{})
+	rtc := ds1307.New(machine.I2C0)
+	rtc.SetTime(time.Date(2019, 5, 15, 20, 34, 12, 0, time.UTC))
+
+	for {
+		t, err := rtc.Time()
+		if err != nil {
+			println("Error reading date:", err)
+			break
+		}
+		println(t.Hour(), ":", t.Minute(), ":", t.Second(), " ", t.Day(), "/", t.Month(), "/", t.Year())
+
+	}
+
+}