Update to latest HTML5lib, Add Maruku testdir

Sync with the latest html5lib.
Having the Maruku unit tests on-hand may be useful for debugging; so let's include them.

vendor/plugins/HTML5lib/lib/html5/serializer/htmlserializer.rb

@@ -31,7 +31,7 @@ module HTML5
       @inject_meta_charset = true
 
       options.each do |name, value|
-        next unless instance_variables.include?("@#{name}")
+        next unless instance_variable_defined?("@#{name}")
         @use_best_quote_char = false if name.to_s == 'quote_char'
         instance_variable_set("@#{name}", value)
       end