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/math/table.md

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+Write a comment here
+*** Parameters: ***
+{}
+*** Markdown input: ***
+<table markdown='1'>
+	$\alpha$
+	<thead>
+		<td>$\beta$</td>
+	</thead>
+</table>
+*** Output of inspect ***
+md_el(:document,[
+	md_html("<table markdown='1'>\n\t$\\alpha$\n\t<thead>\n\t\t<td>$\\beta$</td>\n\t</thead>\n</table>")
+],{},[])
+*** Output of to_html ***
+<table><span class='maruku-inline'><code class='maruku-mathml'>\alpha</code></span><thead>
+		<td><span class='maruku-inline'><code class='maruku-mathml'>\beta</code></span></td>
+	</thead>
+</table>
+*** Output of to_latex ***
+
+*** Output of to_md ***
+
+*** Output of to_s ***
+
+*** EOF ***
+
+
+
+
+Failed tests:   [:to_html] 
+
+*** Output of inspect ***
+md_el(:document,[
+	md_html("<table markdown='1'>\n\t$\\alpha$\n\t<thead>\n\t\t<td>$\\beta$</td>\n\t</thead>\n</table>")
+],{},[])
+*** Output of to_html ***
+-----| WARNING | -----
+<table><span class='maruku-inline'><math class='maruku-mathml' display='inline' xmlns='http://www.w3.org/1998/Math/MathML'><mi>&alpha;</mi></math></span><thead>
+		<td><span class='maruku-inline'><math class='maruku-mathml' display='inline' xmlns='http://www.w3.org/1998/Math/MathML'><mi>&beta;</mi></math></span></td>
+	</thead>
+</table>
+*** Output of to_latex ***
+
+*** Output of to_md ***
+
+*** Output of to_s ***
+
+*** Output of Markdown.pl ***
+<table markdown='1'>
+    $\alpha$
+    <thead>
+        <td>$\beta$</td>
+    </thead>
+</table>
+
+*** Output of Markdown.pl (parsed) ***
+Error: #<NoMethodError: private method `write_children' called for <div> ... </>:REXML::Element>