Moved "Skip to content" link to the top of the #page container making it the first focusable element perceived via screen reader or keyboard navigation. Ensures _s meets accessibility-ready guidelines as per http://make.wordpress.org/themes/guidelines/guidelines-accessibility/
Set height + width to 1px and overflow: hidden to address overflow issue when hidden items are positioned on the right hand side of the screen in Webkit and Opera. Full explanation of problem and solution here: http://snook.ca/archives/html_and_css/hiding-content-for-accessibility
Break declarations into individual lines.
Remove changes to style.css - will be submitted as separate patch.
Aims to create a more hierarchical heading structure. Somewhat based on structure in Twenty Fifteen and inspired by http://blog.rrwd.nl/2014/11/21/html5-headings-in-wordpress-lets-fight/ and https://www.joedolson.com/2014/11/headings-hierarchy-problem/
Merge commit '3a45a8a2decd1090b1bdc172877cade8c0d71795'