Enable post bylines

Just add a `byline:` section to your top-matter to get them.
Update desktop width to 50em
Added {% image %} plugin and styles to look good.

The 'right' class for images makes sexy looking figures.
Fix HTML5 validation error.
Added support for opengraph extensions.
Merge remote-tracking branch 'pjf.github.io/base' into base

Conflicts:
	css/style-desktop.css