Fix unexpected behavior from modified events dict

The events dict is now copied to another temporary variable before the
handler functions are called. This way, if the events dict is changed,
the copy stays in tact, and we don't get unexpected behavior.

pyee/__init__.py

@@ -108,8 +108,12 @@ def emit(self, event, *args, **kwargs):
         """
         handled = False
 
+        # Copy the events dict first. Avoids a bug if the events dict gets
+        # changed in the middle of the following for loop.
+        events_copy = list(self._events[event])
+
         # Pass the args to each function in the events dict
-        for f in self._events[event]:
+        for f in events_copy:
             f(*args, **kwargs)
             handled = True