Small updates for options, added tests

This release is mainly for improving code:

• unified blog_id and blog_url into one option named blog, as per default WordPress OAuth API
• rewritten parts of code for PHP 7
• added tests

More user data

• method for language field

Ready for authenticating users 👍🏼

v1.0

Updated - readme

Into the wild 🐂

Start authenticating your users with their WordPress.com account