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/math_usage/document.md

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+css: math.css
+
+This is an example document. Inline: $a$, $b$, $q$ and stop.
+
+$$        \int_a^b f(x) dx       $$     (1)
+
+See for example (eq:1).
+
+Equation inline: $  \int_a^b f(x) dx $ and that's it.
+
+
+Spacing: Maruku outputs sizes and alignment for images in `ex`. An `ex` is one `x`:
+x, $\textrm{x}$, $x$ should have the same height. 

vendor/plugins/maruku/tests/math_usage/math.css

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+
+body {
+	max-width: 35em;
+}
+
+span.maruku-inline .maruku-mathml  {
+	//display: none;
+}
+
+div.maruku-equation .maruku-mathml  {
+	//display: none;
+}
+
+span.maruku-inline .maruku-png  {
+}
+
+div.maruku-equation .maruku-png  {
+}
+
+div.maruku-equation {
+	text-align: center;
+}
+
+div.maruku-equation span.maruku-eq-number  {
+	display: block; float: right; padding-right: 2em;
+}

vendor/plugins/maruku/tests/math_usage/script.sh

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+
+maruku="ruby -I../../lib ../../bin/maruku"
+
+#input="private.txt"
+input="document.md"
+
+$maruku -m itex2mml -o itex2mml.xhtml $input
+$maruku -m ritex    -o ritex.xhtml  $input
+$maruku -m none     -o none.html  $input
+$maruku -m blahtex  -o blahtex.xhtml  $input
+$maruku -m none    --math-images blahtex  -o blahtexi.html  $input
+$maruku -m blahtex --math-images blahtex  -o blahtexmi.xhtml  $input
+