Added methods to get user infomration for Foursquare and fixed Github API call according to API change.

Hi,

I've added a get_user_information and get_user method for the Foursquare provider to match the other providers and  added an UserAgent in the API call to Github according to an API change. Otherwise it would return a 403 status code. (http://developer.github.com/changes/2013-01-31-user-agent-will-soon-be-mandatory/)

Mathijs.