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/xml3.md

@@ -0,0 +1,44 @@
+Write a comment here
+*** Parameters: ***
+{}
+*** Markdown input: ***
+<table markdown='1'>
+	Blah
+	<thead>
+		<td>*em*</td>
+	</thead>
+</table>
+
+*** Output of inspect ***
+md_el(:document,[
+	md_html("<table markdown='1'>\n\tBlah\n\t<thead>\n\t\t<td>*em*</td>\n\t</thead>\n</table>")
+],{},[])
+*** Output of to_html ***
+<table>Blah<thead>
+		<td><em>em</em></td>
+	</thead>
+</table>
+*** Output of to_latex ***
+
+*** Output of to_md ***
+
+*** Output of to_s ***
+
+*** EOF ***
+
+
+
+	OK!
+
+
+
+*** Output of Markdown.pl ***
+<table markdown='1'>
+    Blah
+    <thead>
+        <td>*em*</td>
+    </thead>
+</table>
+
+*** Output of Markdown.pl (parsed) ***
+Error: #<NoMethodError: private method `write_children' called for <div> ... </>:REXML::Element>