AP_Scripting: add simple example of a loop

libraries/AP_Scripting/examples/simple_loop.lua

@@ -0,0 +1,8 @@
+-- This script is an example of saying hello.  A lot.
+
+function update() -- this is the loop which periodically runs
+  gcs:send_text(0, "hello, world") -- send the traditional message
+  return update, 1000 -- reschedules the loop
+end
+
+return update() -- run immediately before starting to reschedule