added FileSystem infrastructure.

GameRes/ArcFile.cs

@@ -143,6 +143,16 @@ namespace GameRes
             return m_interface.OpenEntry (this, entry);
         }
 
+        /// <summary>
+        /// Open specified <paramref name="entry"/> as memory-mapped view.
+        /// </summary>
+        public ArcView OpenView (Entry entry)
+        {
+            var stream = OpenEntry (entry);
+            uint size = stream.CanSeek ? (uint)stream.Length : entry.Size;
+            return new ArcView (stream, entry.Name, size);
+        }
+
         /// <summary>
         /// Open specified <paramref name="entry"/> as a seekable Stream.
         /// </summary>
@@ -168,6 +178,14 @@ namespace GameRes
             return ArchiveFormat.CreateFile (entry.Name);
         }
 
+        public IFileSystem CreateFileSystem ()
+        {
+            if (m_interface.IsHierarchic)
+                return new ArchiveFileSystem (this);
+            else
+                return new FlatArchiveFileSystem (this);
+        }
+
         #region IDisposable Members
         bool disposed = false;