* new helper: AutoDiscoverRTCClock, which detects: DS3231 (on i2c addr 0x68), or RV3028 (on i2c addr 0x52)

* repeater and room server: ver bump (v5), now use AutoDiscoverRTCClock
* various Board::begin() now should do Wire.begin(), with custom pin mappings if needed
* examples removed: ping client/server, and test_admin

src/helpers/AutoDiscoverRTCClock.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <Mesh.h>
+#include <Arduino.h>
+#include <Wire.h>
+
+class AutoDiscoverRTCClock : public mesh::RTCClock {
+  mesh::RTCClock* _fallback;
+
+  bool i2c_probe(TwoWire& wire, uint8_t addr);
+public:
+  AutoDiscoverRTCClock(mesh::RTCClock& fallback) : _fallback(&fallback) { }
+
+  void begin(TwoWire& wire);
+  uint32_t getCurrentTime() override;
+  void setCurrentTime(uint32_t time) override;
+};