Add small example program

.gitignore

+*.o
+/*.elf
+/*.hex

example.cpp

+#include <BOB3.h>
+
+void setup()
+{
+  bob3.enableIRSensor(true);
+}
+
+void loop()
+{
+  int16_t proximity = bob3.getIRSensor();
+  int16_t red = proximity;
+  int16_t green = 15 - proximity;
+  green = green < 0 ? 0 : green;
+  uint16_t color = rgb(red, green, 0);
+  bob3.setEyes(color, color);
+
+  bob3.setWhiteLeds(bob3.getArm(1), bob3.getArm(2));
+}