Tweaks to improve the mobile ready site

Changed footer_content class to footer-content
Changed secondary content from an aside to a section tagline
Changed the header to have a min-height of 180px so on small screens it grows to
accommodate the full site title
Changed the content section to full width, and the primary & secondary content
sections within to be max width 80em
Adjusted the padding and margins on entries, entry headings, wdigets etc to
improve the look of the site
Changed the class of the author meta details from byline to entry-author