use proper notation for true, false, and null in doc comments

sdk/lib/io/data_transformer.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 
 /**
  * An instance of the default implementation of the [ZLibCodec].
  */
@@ skipping 247 matching lines @@
 }
 
 
 
 /**
  * Private helper-class to handle native filters.
  */
 abstract class _Filter {
   /**
    * Call to process a chunk of data. A call to [process] should only be made
-   * when [processed] returns [null].
+   * when [processed] returns [:null:].
    */
   void process(List<int> data, int start, int end);
 
   /**
    * Get a chunk of processed data. When there are no more data available,
-   * [processed] will return [null]. Set [flush] to [false] for non-final
+   * [processed] will return [:null:]. Set [flush] to [:false:] for non-final
    * calls to improve performance of some filters.
    *
-   * The last call to [processed] should have [end] set to [true]. This will make
+   * The last call to [processed] should have [end] set to [:true:]. This will make
    * sure a 'end' packet is written on the stream.
    */
   List<int> processed({bool flush: true, bool end: false});
 
   /**
    * Mark the filter as closed. Always call this method for any filter created
    * to avoid leaking resources. [end] can be called at any time, but any
    * successive calls to [process] or [processed] will fail.
    */
   void end();
 
   external static _Filter newZLibDeflateFilter(bool gzip, int level);
   external static _Filter newZLibInflateFilter();
 }