Add support for explicitly ignoring doctype

Author: wooorm

lib/handlers/index.js

@@ -7,6 +7,8 @@ exports.root = require('./root');
 exports.text = require('./text');
 exports.comment = require('./comment');
 
+exports.doctype = ignore;
+
 exports.area =
 exports.basefont =
 exports.bgsound =