Follow up to previous commit.

* Expose is_tablet property to events to determine if event contains
tablet data.
* Expose tablet tilt for events as a 2D vector in python

source/blender/windowmanager/WM_api.h

@@ -449,7 +449,8 @@ void        WM_event_ndof_rotate_get(const struct wmNDOFMotionData *ndof, float
 float       WM_event_ndof_to_axis_angle(const struct wmNDOFMotionData *ndof, float axis[3]);
 void        WM_event_ndof_to_quat(const struct wmNDOFMotionData *ndof, float q[4]);
 
-float       WM_event_tablet_data(const struct wmEvent *event, int *pen_flip);
+float       WM_event_tablet_data(const struct wmEvent *event, int *pen_flip, float tilt[2]);
+bool        WM_event_is_tablet(const struct wmEvent *event);
 
 #ifdef __cplusplus
 }