add SerializeToLonLat function and switch web calls to use that

src/Geocoding/ForwardGeocodeResource.cs

@@ -148,7 +148,7 @@ public override string GetUrl()
 			if (this.Proximity != null)
 			{
 				var nonNullableProx = (Vector2d)this.Proximity;
-				opts.Add("proximity", nonNullableProx.ToString());
+				opts.Add("proximity", nonNullableProx.SerializeToLonLat());
 			}
 
 			if (this.Types != null)

src/Geocoding/ReverseGeocodeResource.cs

@@ -47,7 +47,7 @@ public override string GetUrl()
 			return Constants.BaseAPI +
 							this.ApiEndpoint +
 							this.Mode +
-							this.Query.ToString() +
+							this.Query.SerializeToLonLat() +
 							".json" +
 							EncodeQueryString(opts);
 		}

src/Utils/GeoCoordinateBounds.cs

@@ -167,7 +167,7 @@ public double[] ToArray()
 		/// <returns> Returns a string for use in a Mapbox query URL. </returns>
 		public override string ToString()
 		{
-			return string.Format("{0},{1}", this.SouthWest.ToString(), this.NorthEast.ToString());
+			return string.Format("{0},{1}", this.SouthWest.SerializeToLonLat(), this.NorthEast.SerializeToLonLat());
 		}
 	}
 }

src/Utils/Vector2d/Vector2d.cs

@@ -186,6 +186,11 @@ public void Normalize()
         }
 
         public override string ToString()
+        {
+            return string.Format(NumberFormatInfo.InvariantInfo, "{0:F5},{1:F5}", this.x, this.y);
+        }
+
+        public string SerializeToLonLat()
         {
             return string.Format(NumberFormatInfo.InvariantInfo, "{0:F5},{1:F5}", this.y, this.x);
         }