switch html5lib to new pkg layout

lib/src/treebuilder.dart

Index: lib/src/treebuilder.dart
diff --git a/treebuilders/base.dart b/lib/src/treebuilder.dart
similarity index 98%
rename from treebuilders/base.dart
rename to lib/src/treebuilder.dart
index 9806c5a7cd04f05a69f4b3a5e969504dd90a1293..879e1717a93b45d437b2e59ed3b33a415d8f173b 100644
--- a/treebuilders/base.dart
+++ b/lib/src/treebuilder.dart
@@ -1,11 +1,11 @@
 /** Internals to the tree builders. */
-#library('base');
+#library('treebuilder');
 
-#import('../lib/constants.dart');
-#import('../lib/list_proxy.dart');
-#import('../lib/token.dart');
-#import('../lib/utils.dart');
-#import('simpletree.dart');
+#import('constants.dart');
+#import('list_proxy.dart');
+#import('token.dart');
+#import('utils.dart');
+#import('../dom.dart');
 
 // The scope markers are inserted when entering object elements,
 // marquees, table cells, and table captions, and are used to prevent formatting