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/MarkdownTest_1.0/Tests/Amps and angle encoding.text

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+AT&T has an ampersand in their name.
+
+AT&T is another way to write it.
+
+This & that.
+
+4 < 5.
+
+6 > 5.
+
+Here's a [link][1] with an ampersand in the URL.
+
+Here's a [link] [1] with an ampersand in the URL.
+
+Here's a link with an amersand in the link text: [AT&T] [2].
+
+Here's an inline [link](/script?foo=1&bar=2).
+
+Here's an inline [link](</script?foo=1&bar=2>).
+
+
+[1]: http://example.com/?foo=1&bar=2
+[2]: http://att.com/  "AT&T"