Add Bounce2 header to examples. Due to an annoying quirk with Arduino, we only include library headers directly referenced by the sketch, so dependencies have to be listed explicitly.

examples/switch_panel_improved/switch_panel_improved.ino

@@ -1,6 +1,7 @@
 // This is the same 5-toggle-switch example from switch_panel.ino, using the
 // new API. So much easier!
 
+#include <Bounce2.h>
 #include <Joystick.h>
 
 Joystick joystick;