Added tiff support.

NTwain/Interop/TIFF.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+
+namespace NTwain.Interop
+{
+    // this is from twain cs sample
+    // http://sourceforge.net/projects/twainforcsharp/?source=typ_redirect
+
+    /// <summary>
+    /// The TIFF file header.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    struct TIFFHEADER
+    {
+        public ushort u8ByteOrder;
+        public ushort u16Version;
+        public uint u32OffsetFirstIFD;
+        public ushort u16u16IFD;
+    }
+
+    /// <summary>
+    /// An individual TIFF Tag.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    struct TIFFTAG
+    {
+        public ushort u16Tag;
+        public ushort u16Type;
+        public uint u32Count;
+        public uint u32Value;
+    }
+}