Deprecating WaitForResult()

Resolves #19

src/Postmark.PCL/TaskExtensions.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System;
+using System.Threading.Tasks;
 
 namespace PostmarkDotNet
 {
@@ -8,10 +9,21 @@ public static class TaskExtensions
         /// <summary>
         /// Escape async/await by runing the task synchronously, 
         /// will block the current thread until the task completes.
+        /// 
+        /// DO NOT USE THIS IN A UI THREAD.
+        /// It will cause your application to become deadlocked.
+        /// <see cref="http://blogs.msdn.com/b/pfxteam/archive/2011/01/13/10115163.aspx"/>
         /// </summary>
+        /// <remarks>
+        /// You should avoid using this method in new code. If you're unable to use async/await support,
+        /// consider using "ContinueWith()" <see cref="https://msdn.microsoft.com/en-us/library/dd321474(v=vs.110).aspx"/> 
+        /// in order to ensure proper sequencing operations.
+        /// </remarks>
         /// <typeparam name="T"></typeparam>
         /// <param name="task"></param>
         /// <returns></returns>
+        [Obsolete("This convenience method has been deprecated" +
+            " because it is known cause issues in specific use cases.")]
         public static T WaitForResult<T>(this Task<T> task)
         {
             task.Wait();