add i2c master scan

Author: hathach

libraries/Wire/examples/master_scan/master_scan.ino

@@ -0,0 +1,28 @@
+#include <Wire.h>
+
+TwoWire *wi = &Wire;
+//TwoWire *wi = &Wire1;
+
+void setup()
+{
+  Serial.begin(115200);  // start serial for output
+  while ( !Serial ) delay(10);   // for nrf52840 with native usb
+  wi->begin();        // join i2c bus (address optional for master)
+}
+
+void loop()
+{
+  Serial.println("Scanning address from 0 to 127");
+  for (int addr = 1; addr < 128; addr++)
+  {
+    wi->beginTransmission(addr);
+    if ( 0 == wi->endTransmission() )
+    {
+      Serial.print("Found: 0x");
+      Serial.print(addr, HEX);
+      Serial.println();
+    }
+  }
+
+  delay(5000);
+}