Checked all methods for:

* proper html, i.e. "..." not '...' for attributes
* avoiding sending empty tags - especially with all the filters, you never know whether they are used properly
* proper use of esc_attr()/esc_url()
Oh dear.. typos
Merge branch 'master' of git://github.com/jdevalk/wordpress-seo into Fix-no-empty-twitter-tags

Conflicts:
	readme.txt
Merge pull request #120 from jrfnl/Fix-no-empty-twitter-tags

Fix no empty twitter tags