switch html5lib to new pkg layout

test/parser_test.dart

 #library('parser_test');
 
 #import('dart:io');
 #import('package:unittest/unittest.dart');
 #import('package:unittest/vm_config.dart');
-#import('../lib/constants.dart');
-#import('../lib/utils.dart');
-#import('../treebuilders/simpletree.dart');
-#import('../html5parser.dart');
-#import('../tokenizer.dart');
+#import('package:html5lib/src/constants.dart');
+#import('package:html5lib/src/utils.dart');
+#import('package:html5lib/dom.dart');
+#import('package:html5lib/html5parser.dart');
+#import('package:html5lib/tokenizer.dart');
 #import('support.dart');
 
 // Run the parse error checks
 // TODO(jmesserly): presumably we want this on by default?
 final checkParseErrors = false;
 
 String namespaceHtml(String expected) {
   // TODO(jmesserly): this is a workaround for http://dartbug.com/2979
   // We can't do regex replace directly =\
   // final namespaceExpected = const RegExp(@"^(\s*)<(\S+)>", multiLine: true);
@@ skipping 85 matching lines @@
               });
             }
           }
 
           index++;
         }
       });
     }
   });
 }