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/maruku/tests/unittest/headers.md

@@ -0,0 +1,54 @@
+Write a comment abouth the test here.
+*** Parameters: ***
+{:title=>"A title with emphasis"}
+*** Markdown input: ***
+A title with *emphasis*
+=======================
+
+A title with *emphasis*
+-----------------------
+
+
+#### A title with *emphasis* ####
+
+
+
+*** Output of inspect ***
+md_el(:document,[
+	md_el(:header,["A title with ", md_em(["emphasis"])],{:level=>1},[]),
+	md_el(:header,["A title with ", md_em(["emphasis"])],{:level=>2},[]),
+	md_el(:header,["A title with ", md_em(["emphasis"])],{:level=>4},[])
+],{},[])
+*** Output of to_html ***
+<h1 id='a_title_with_emphasis'>A title with <em>emphasis</em></h1>
+
+<h2 id='a_title_with_emphasis'>A title with <em>emphasis</em></h2>
+
+<h4 id='a_title_with_emphasis'>A title with <em>emphasis</em></h4>
+*** Output of to_latex ***
+\hypertarget{a_title_with_emphasis}{}\section*{{A title with \emph{emphasis}}}\label{a_title_with_emphasis}
+
+\hypertarget{a_title_with_emphasis}{}\subsection*{{A title with \emph{emphasis}}}\label{a_title_with_emphasis}
+
+\hypertarget{a_title_with_emphasis}{}\paragraph*{{A title with \emph{emphasis}}}\label{a_title_with_emphasis}
+*** Output of to_md ***
+A title with emphasisA title with emphasisA title with emphasis
+*** Output of to_s ***
+A title with emphasisA title with emphasisA title with emphasis
+*** EOF ***
+
+
+
+	OK!
+
+
+
+*** Output of Markdown.pl ***
+<h1>A title with <em>emphasis</em></h1>
+
+<h2>A title with <em>emphasis</em></h2>
+
+<h4>A title with <em>emphasis</em></h4>
+
+*** Output of Markdown.pl (parsed) ***
+Error: #<NoMethodError: private method `write_children' called for <div> ... </>:REXML::Element>