more efficient encoding for lat/lon

mesh.proto

@@ -76,8 +76,8 @@ message Position {
 
   /** The new preferred location encoding, divide by 10e-7 to get degrees in
    * floating point */
-  int32 latitude_i = 7;
-  int32 longitude_i = 8;
+  sint32 latitude_i = 7;
+  sint32 longitude_i = 8;
 
   int32 altitude = 3;
   int32 battery_level = 4; // 1-100 (0 means not provided)