Added named state enum.

NTwain/State.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace NTwain
+{
+    /// <summary>
+    /// The logical state of a TWAIN session.
+    /// </summary>
+    public enum State
+    {
+        /// <summary>
+        /// The starting state, corresponds to state 1.
+        /// </summary>
+        DsmUnloaded = 1,
+        /// <summary>
+        /// The DSM library has been loaded, corresponds to state 2.
+        /// </summary>
+        DsmLoaded = 2,
+        /// <summary>
+        /// The DSM has been opened, corresponds to state 3.
+        /// </summary>
+        DsmOpened = 3,
+        /// <summary>
+        /// A data source has been opened, corresponds to state 4.
+        /// </summary>
+        SourceOpened = 4,
+        /// <summary>
+        /// A data source has been enabled, corresponds to state 5.
+        /// </summary>
+        SourceEnabled = 5,
+        /// <summary>
+        /// Data is ready for transfer from the source, corresponds to state 6.
+        /// </summary>
+        TransferReady = 6,
+        /// <summary>
+        /// Data is being transferred, corresponds to state 7.
+        /// </summary>
+        Transferring = 7
+    };
+
+}