Enrich twitter username validation documentation
Don't nest what doesn't need nesting
Simplify admin menu access determination
Merge branch 'master' of git://github.com/Yoast/wordpress-seo into Mini-tweaks

Conflicts:
	inc/wpseo-non-ajax-functions.php
Merge branch 'master' of git://github.com/Yoast/wordpress-seo into Mini-tweaks
Remove left over brace
Apply sitemap user role filter consistently
Move remove_excluded_authors function to a more logical place
Move wpseo_get_roles() to be in active functions, rather than deprecated
Fix links breaking for protocol relative links
Move some non-changing variables out of a double loop (efficiency)

Also ensure the scheme used for images in the sitemap is the same as used for the site
Whitespace
Consistency in the logic for the image urls in the sitemap
Removed the user role filtering on admin after all
Merge pull request #1431 from jrfnl/Mini-tweaks

Various mini tweaks, props @jrfnl