Refactor OpenGraph class to use one internal function `og_tag` for output.
Add support for OpenGraph publication date, last modified date, tags and categories, mostly because [Pinterest added support for article tags](http://blog.pinterest.com/post/62158724907/find-and-save-great-reads-with-new-article-pins).
Prevent outputting `[&hellip;]` by replacing it with `&hellip;`
Add upload for Facebook image to Social tab.
Rename `objectL10n` to `wpseoL10n`, fixes #263.
Fix `og:sitename`, should be `go:site_name`.
Better naming for the L10n object
Make the custom image uploader work when there are several uploaders in WP SEO metaboxes
Properly namespace the used variables
Updated read me with recent changes.