Restructure YAML package suitable for pub lish

utils/pub/yaml/lib/parser.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Translates a string of characters into a YAML serialization tree.
  *
  * This parser is designed to closely follow the spec. All productions in the
  * spec are numbered, and the corresponding methods in the parser have the same
  * numbers. This is certainly not the most efficient way of parsing YAML, but it
@@ skipping 1979 matching lines @@
       var pair = contents[i];
       if (pair.first.contains(pos)) return pair.last;
     }
     return null;
   }
 
   /** Associates [value] with [range]. */
   operator[]=(_Range range, E value) =>
     contents.add(new _Pair<_Range, E>(range, value));
 }