Added a sitemap at the insistance of Google Webmaster Tools. My version is based heavily on David Ensinger's: http://davidensinger.com/2013/11/building-a-better-sitemap-xml-with-jekyll/
Overhauled the site to use HTML5 semantic markup.
Switching to semantic markup broke the responsive design elements.
Mistook Jekyll's page and post variables.
Fixed a couple of rendering issues that caused <pre> blocks to display incorrectly in Firefox.
Added html5shiv script so semantic markup will work with older versions of Internet Explorer.
Updated 404 page to use semantic markup. Because, why not?