add Web-Hook alert support

UptimeSharp.Tests/AlertsTest.cs

@@ -55,14 +55,17 @@ namespace UptimeSharp.Tests
     {
       Alert alert1;
       Alert alert2;
+      Alert alert3;
 
       Assert.NotNull(alert1 = await client.AddAlert(AlertType.Email, "example1@ceecore.com"));
       Assert.NotNull(alert2 = await client.AddAlert(AlertType.Boxcar, "example2@ceecore.com"));
+      Assert.NotNull(alert3 = await client.AddAlert(AlertType.WebHook, "http://ceecore.com?"));
 
       try
       {
         await client.DeleteAlert(alert1);
         await client.DeleteAlert(alert2);
+        await client.DeleteAlert(alert3);
       }
       catch { }
     }

UptimeSharp/Components/Alert.cs

@@ -45,7 +45,7 @@ namespace UptimeSharp
 
     /// <summary>
     /// Adds an alert.
-    /// mobile/SMS alert contacts are not supported yet, see: http://www.uptimerobot.com/api.asp#methods
+    /// SMS & Twitter alert contacts are not supported yet, see: http://www.uptimerobot.com/api.asp#methods
     /// </summary>
     /// <param name="type">The type.</param>
     /// <param name="value">The value.</param>

UptimeSharp/Models/Alert.cs

@@ -90,7 +90,11 @@ namespace UptimeSharp.Models
     /// <summary>
     /// Boxcar
     /// </summary>
-    Boxcar = 4
+    Boxcar = 4,
+    /// <summary>
+    /// Web Hook
+    /// </summary>
+    WebHook = 5
   }