Added SDL_GetDisplayOrientation() to get the display orientation, and added a new event SDL_DISPLAYEVENT to notify the application when the orientation changes.

Documented the values returned by the accelerometer and gyroscope sensors

src/dynapi/SDL_dynapi_overrides.h

@@ -695,3 +695,4 @@
 #define SDL_SensorClose SDL_SensorClose_REAL
 #define SDL_SensorUpdate SDL_SensorUpdate_REAL
 #define SDL_IsTablet SDL_IsTablet_REAL
+#define SDL_GetDisplayOrientation SDL_GetDisplayOrientation_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -737,3 +737,4 @@ SDL_DYNAPI_PROC(int,SDL_SensorGetData,(SDL_Sensor *a, float *b, int c),(a,b,c),r
 SDL_DYNAPI_PROC(void,SDL_SensorClose,(SDL_Sensor *a),(a),)
 SDL_DYNAPI_PROC(void,SDL_SensorUpdate,(void),(),)
 SDL_DYNAPI_PROC(SDL_bool,SDL_IsTablet,(void),(),return)
+SDL_DYNAPI_PROC(SDL_DisplayOrientation,SDL_GetDisplayOrientation,(int a),(a),return)