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/equations.md

@@ -0,0 +1,69 @@
+Write a comment here
+*** Parameters: ***
+{}
+*** Markdown input: ***
+
+$$ x = y $$
+
+$$ x 
+= y $$
+
+$$ 
+x = y $$
+
+$$ x = y 
+$$
+
+*** Output of inspect ***
+md_el(:document,[
+	md_par(["$$ x = y $$"]),
+	md_el(:header,["$$ x"],{:level=>1},[]),
+	md_par(["$$ x = y $$"]),
+	md_par(["$$ x = y $$"])
+],{},[])
+*** Output of to_html ***
+<p>$$ x = y $$</p>
+
+<h1 id='_x'>$$ x</h1>
+
+<p>$$ x = y $$</p>
+
+<p>$$ x = y $$</p>
+*** Output of to_latex ***
+\$\$ x = y \$\$
+
+\hypertarget{_x}{}\section*{{\$\$ x}}\label{_x}
+
+\$\$ x = y \$\$
+
+\$\$ x = y \$\$
+*** Output of to_md ***
+$$ x = y $$
+
+$$ x$$ x = y $$
+
+$$ x = y $$
+*** Output of to_s ***
+$$ x = y $$$$ x$$ x = y $$$$ x = y $$
+*** EOF ***
+
+
+
+	OK!
+
+
+
+*** Output of Markdown.pl ***
+<p>$$ x = y $$</p>
+
+<p>$$ x 
+= y $$</p>
+
+<p>$$ 
+x = y $$</p>
+
+<p>$$ x = y 
+$$</p>
+
+*** Output of Markdown.pl (parsed) ***
+Error: #<NoMethodError: private method `write_children' called for <div> ... </>:REXML::Element>