Work history, education and skills

Hello,

First of all, congrats on a very useful and well written library. I'd like to contribute by developing a couple of new features we need:

Hybrid_Provider_Model->getUserWorkHistory()
Hybrid_Provider_Model->getUserEducation()
Hybrid_Provider_Model->getUserSkills()

These would work in a similar way to getUserProfile and getUserContacts. The initial implementation will be for Facebook/Linkedin

See the attached pull request.

Sorin