In addition to the substitute command (s,from, to,[g]) it is possible to
limit the search/replace to specific symbols, in order to refactor the
namings without touching other symbols.
For example: %state,from,to, will change only the text in the state
symbols

%s,from,to,g -> g is global across all scenes

1) translate_to_origin was using symbol coordinates instead of scene
coordinates so there could still be negative coordinates
2) render_everything was badly testing the input ast coordinates

Continuous signals have less priority than inputs. Therefore before
evaluating them it is mandatory to check the presence of messages in the
input queue of the SDL process. User has to provide the function that
checks the queue. TASTE uses POHIC API for that.