New method get_user() for Facebook and Google

/src/OAuth2/Provider/Facebook.php
/src/OAuth2/Provider/Google.php
-se.Added new method called get_user() which returns the entire contents
of the provider response for Facebook and Google.
Added get_user() to GitHub, Mailchimp, and Windowslive

/src/OAuth2/Provider/Github.php
/src/OAuth2/Provider/Mailchimp.php
/src/OAuth2/Provider/Windowslive.php
-Added get_user() to the above-mentioned files which returns the entire
contents of the response.
Updated get_user()

/src/OAuth2/Provider/Facebook.php
/src/OAuth2/Provider/Github.php
/src/OAuth2/Provider/Mailchimp.php
/src/OAuth2/Provider/Windowslive.php
-The data retrieved from get_user() is being returned in the form of an
array.
Merge pull request #7 from koufax/master

Added method get_user() for several providers