adding fusion docs and tests

[SVN r34920]

example/extension/detail/begin_impl.hpp

@@ -0,0 +1,41 @@
+/*=============================================================================
+    Copyright (c) 2001-2006 Joel de Guzman
+    Copyright (c) 2005-2006 Dan Marsden
+
+    Use, modification and distribution is subject to the Boost Software
+    License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+    http://www.boost.org/LICENSE_1_0.txt)
+==============================================================================*/
+#if !defined(BOOST_FUSION_BEGIN_IMPL_20060222_2042)
+#define BOOST_FUSION_BEGIN_IMPL_20060222_2042
+
+#include "../example_struct_iterator.hpp"
+
+namespace boost { namespace fusion {
+    
+    struct example_sequence_tag;
+
+    namespace extension
+    {
+        template<typename Tag>
+        struct begin_impl;
+
+        template<>
+        struct begin_impl<example_sequence_tag>
+        {
+            template<typename Sequence>
+            struct apply
+            {
+                typedef example_struct_iterator<Sequence, 0> type;
+
+                static type
+                call(Sequence& seq)
+                {
+                    return type(seq);
+                }
+            };
+        };
+    }
+}}
+
+#endif