add DS1307RTC support

DS1307RTC/examples/ReadTest/ReadTest.ino

@@ -0,0 +1,49 @@
+#include <Wire.h>
+#include <TimeLib.h>
+#include <DS1307RTC.h>
+
+void setup() {
+  Serial.begin(9600);
+  while (!Serial) ; // wait for serial
+  delay(200);
+  Serial.println("DS1307RTC Read Test");
+  Serial.println("-------------------");
+}
+
+void loop() {
+  tmElements_t tm;
+
+  if (RTC.read(tm)) {
+    Serial.print("Ok, Time = ");
+    print2digits(tm.Hour);
+    Serial.write(':');
+    print2digits(tm.Minute);
+    Serial.write(':');
+    print2digits(tm.Second);
+    Serial.print(", Date (D/M/Y) = ");
+    Serial.print(tm.Day);
+    Serial.write('/');
+    Serial.print(tm.Month);
+    Serial.write('/');
+    Serial.print(tmYearToCalendar(tm.Year));
+    Serial.println();
+  } else {
+    if (RTC.chipPresent()) {
+      Serial.println("The DS1307 is stopped.  Please run the SetTime");
+      Serial.println("example to initialize the time and begin running.");
+      Serial.println();
+    } else {
+      Serial.println("DS1307 read error!  Please check the circuitry.");
+      Serial.println();
+    }
+    delay(9000);
+  }
+  delay(1000);
+}
+
+void print2digits(int number) {
+  if (number >= 0 && number < 10) {
+    Serial.write('0');
+  }
+  Serial.print(number);
+}