Emergency stop script execute

[theludovyc]

We cannot kill thread in Godot. Only way it is quit them properly.

Call Rakugo.execute_script(script_name) or Rakugo.parse_and_execute(file_name), start a thread to read and execute RakuScript.

Currently we should finish all script reading to finish execution. We cannot interrupt it in the middle.

I propose to add a method to Rakugo, like "Rakugo.emergency_stop_script(script_name)`, to interrupt execution in case it need.

Of course, signal "on_execute_script_finished" is send, in all cases.

[Jeremi360]

This is a good idea