Added quickie to open a source.

NTwain/ITwainSession.cs

@@ -81,6 +81,13 @@ namespace NTwain
         /// <returns></returns>
         IEnumerable<TwainSource> GetSources();
 
+        /// <summary>
+        /// Quick shortcut to open a source.
+        /// </summary>
+        /// <param name="sourceName">Name of the source.</param>
+        /// <returns></returns>
+        ReturnCode OpenSource(string sourceName);
+
         /// <summary>
         /// Gets the manager status. Only call this at state 2 or higher.
         /// </summary>