New pntpos output

few changes:

• from int pos_stat (0 or 1) to bool success
• added std::string msg for failing message

include/gnss_utils/gnss_utils.h

@@ -42,7 +42,8 @@ struct ComputePosOutput
   double          age;        // age of differential (s)
   double          ratio;      // AR ratio factor for valiation
 
-  int             pos_stat;  // return from pntpos 1:ok,0:error
+  bool            success;   // return from pntpos true/false
+  std::string     msg;       // message returned (in case of error)
   Eigen::Vector3d lat_lon;   // latitude_longitude_altitude
 
   std::map<int,Eigen::Vector2d> sat_azel; // azimuth and elevation of each satellite provided