change to normalized uint8 frames sent from producer to consumer.

added prefs util to make life easier for some utils using fileopenbox and diropenbox from easygui.
add comments about polarity of events that might be helpful.

pyaer/davis.py

@@ -1336,7 +1336,7 @@ def get_event(self, mode="events"):
                 The second number is the X position of the event.
                 The third number is the Y position of the event.
                 The fourth number represents the polarity of the event
-                (positive or negative).<br/>
+                (OFF,ON) = (0,1) (Note these values are NOT (-1,+1).
                 If the `noise_filter` option is set to `True`,
                 this array has an additional column at the end.
                 The last column represents the validity of the corresponding