AP_Scripting: add i2c scan example

libraries/AP_Scripting/examples/i2c_scan.lua

@@ -0,0 +1,27 @@
+-- This script scans for devices on the i2c bus
+local address = 0
+local found = 0
+
+local i2c_bus = i2c.get_device(0,0)
+i2c_bus:set_retries(10)
+
+function update() -- this is the loop which periodically runs
+
+  i2c_bus:set_address(address)
+
+  if i2c_bus:read_registers(0) then
+      gcs:send_text(0, "Found I2C at " .. tostring(address))
+      found = found + 1
+  end
+
+  address = address + 1
+  if address == 127 then
+    address = 0
+    gcs:send_text(0, "Found " .. tostring(found) .. " devices")
+    found = 0
+  end
+
+  return update, 100 -- reschedules the loop
+end
+
+return update() -- run immediately before starting to reschedule