switch html5lib to new pkg layout

lib/dom.dart

Index: lib/dom.dart
diff --git a/treebuilders/simpletree.dart b/lib/dom.dart
similarity index 99%
rename from treebuilders/simpletree.dart
rename to lib/dom.dart
index 8361e2bd505ce1616363715d5b312f40cff3dd7e..c8b5b8c0040b88aff8794d658d1c1439567eea61 100644
--- a/treebuilders/simpletree.dart
+++ b/lib/dom.dart
@@ -2,11 +2,11 @@
  * A simple tree API that results from parsing html. Intended to be compatible
  * with dart:html, but right now it resembles the classic JS DOM.
  */
-#library('simpletree');
+#library('dom');
 
-#import('../lib/constants.dart');
-#import('../lib/utils.dart');
-#import('base.dart');
+#import('src/constants.dart');
+#import('src/treebuilder.dart');
+#import('src/utils.dart');
 
 class Span {
   /** The line of this span. 1-based. */