Add halsim unit tests (#783)

Also adds function that can register all the callbacks at once.
Since all of the callbacks issue a string identifier, it makes it
possible and easy to have one function callback, and differentiate the
path to take based on the string.  Hooking up all the callbacks at once
makes it easier for the simulator developer to know when something was
added to wpilib rather than looking at the commits.

hal/src/main/native/include/MockData/DriverStationData.h

@@ -86,6 +86,10 @@ void HALSIM_RegisterDriverStationAllCallbacks(HAL_NotifyCallback callback,
 
 void HALSIM_NotifyDriverStationNewData(void);
 
+void HALSIM_RegisterDriverStationAllCallbacks(HAL_NotifyCallback callback,
+                                              void* param,
+                                              HAL_Bool initialNotify);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif