+minetest.is_yes(arg) (possible in async calls)
+^ returns whether arg can be interpreted as yes
+
+Async:
+engine.handle_async(async_job,parameters,finished)
+^ execute a function asynchronously
+^ async_job is a function receiving one parameter and returning one parameter
+^ parameters parameter table passed to async_job
+^ finished function to be called once async_job has finished
+^ the result of async_job is passed to this function
+
+Limitations of Async operations
+ -No access to global lua variables, don't even try
+ -Limited set of available functions
+ e.g. No access to functions modifying menu like engine.start,engine.close,
+ engine.file_open_dialog
+