Hello: example fix travis warning

missing function declaration
implicit cast
some style fix

Tools/Hello/Hello.cpp

@@ -5,6 +5,9 @@
 
 #include <AP_HAL/AP_HAL.h>
 
+void setup();
+void loop();
+
 const AP_HAL::HAL& hal = AP_HAL::get_HAL();
 
 void setup()