Added specs and code for #has_friend_request_from?

Added this method to check if a user has a friend request.  It
in the same line as the #is_friends_with? method.  Also used it
to make the #ignore_friend_request and #approve_friend_request
methods a bit more readable.
Merge pull request #4 from jphager2/friendable

Added specs and code for #has_friend_request_from?