Revert "Remove Piwik tracking code"

This reverts commit aa12783.

Author: strugee

src/includes/footer.pug

@@ -1,3 +1,21 @@
 footer
 	p You may find the source code for this website, licensed to you under the GNU Affero GPL, <a rel="license" href="https://github.com/strugee/strugee.github.com">on GitHub</a>. English copy is additionally licensed under <a rel="license" href="https://creativecommons.org/licenses/by-sa/4.0/">Creative Commons BY-SA 4.0</a>.
 	p &copy; Copyright 2012-2019 AJ Jordan.
+
+// Piwik
+// Note that this Piwik instance is self-hosted and so doesn't leak metadata. Also, critically, it respects Do Not Track.
+script.
+	var _paq = _paq || [];
+	_paq.push(['trackPageView']);
+	_paq.push(['enableLinkTracking']);
+	(function() {
+	var u="//piwik.strugee.net/";
+	_paq.push(['setTrackerUrl', u+'piwik.php']);
+	_paq.push(['setSiteId', 1]);
+	var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
+	g.type='text/javascript'; g.async=true; g.defer=true; g.src=u+'piwik.js'; s.parentNode.insertBefore(g,s);
+	})();
+noscript
+	p
+		img(src="//piwik.strugee.net/piwik.php?idsite=1", style="border:0;", alt="")
+// End Piwik Code