switch html5lib to new pkg layout

lib/token.dart

-/** This library contains token types used by the html5 tokenizer. */
-#library('token');
-
-/** An html5 token. */
-class Token {
-  abstract int get kind;
-
-  // TODO(jmesserly): it'd be nice to remove this and always use the ".data"
-  // on the particular token type.
-  abstract get data;
-  abstract set data(value);
-}
-
-class TagToken extends Token {
-  String name;
-
-  // TODO(jmesserly): this starts as a List, but becomes a Map of attributes.
-  // Should probably separate these into different named fields.
-  var data;
-
-  bool selfClosing;
-
-  TagToken(this.name, data, this.selfClosing)
-      : data = data == null ? [] : data;
-}
-
-class StartTagToken extends TagToken {
-  bool selfClosingAcknowledged;
-
-  /** The namespace. This is filled in later during tree building. */
-  String namespace;
-
-  StartTagToken([String name, data, bool selfClosing = false,
-      this.selfClosingAcknowledged = false, this.namespace])
-      : super(name, data, selfClosing);
-
-  int get kind => TokenKind.startTag;
-}
-
-class EndTagToken extends TagToken {
-
-  EndTagToken([String name, data, bool selfClosing = false])
-      : super(name, data, selfClosing);
-
-  int get kind => TokenKind.endTag;
-}
-
-class StringToken extends Token {
-  String data;
-  StringToken(this.data);
-}
-
-class ParseErrorToken extends StringToken {
-  /** Extra information that goes along with the error message. */
-  Map messageParams;
-
-  ParseErrorToken([String data, this.messageParams]) : super(data);
-
-  int get kind => TokenKind.parseError;
-}
-
-class CharactersToken extends StringToken {
-  CharactersToken([String data]) : super(data);
-
-  int get kind => TokenKind.characters;
-}
-
-class SpaceCharactersToken extends StringToken {
-  SpaceCharactersToken([String data]) : super(data);
-
-  int get kind => TokenKind.spaceCharacters;
-}
-
-class CommentToken extends StringToken {
-  CommentToken([String data]) : super(data);
-
-  int get kind => TokenKind.comment;
-}
-
-class DoctypeToken extends Token {
-  String publicId;
-  String systemId;
-  String name;
-  bool correct;
-
-  DoctypeToken([this.publicId, this.systemId, this.correct = false])
-      : name = "";
-
-  int get kind => TokenKind.doctype;
-
-  // TODO(jmesserly): remove. These are only here because of Token.data
-  String get data { throw const UnsupportedOperationException("data"); }
-  set data(value) { throw const UnsupportedOperationException("data"); }
-}
-
-
-class TokenKind {
-  static const int spaceCharacters = 0;
-  static const int characters = 1;
-  static const int startTag = 2;
-  static const int endTag = 3;
-  static const int comment = 4;
-  static const int doctype = 5;
-  static const int parseError = 6;
-}