def exists?(nickname)
      users.each do |user|
        if user.nickname == nickname
          return true;
        end
      end

      false
    end
def exists?(nickname)
      users.each do |user|
        if user.nickname == nickname
          return true;
        end
      end

      false
    end
Initializes the object. If no users are supplied we look for a config file, if none then create it, and parse it to load users
 @param [String] config_file The path to the file that stores users
 Checks if a user with _nickname_ exists
 @param [String] nickname
 @return [Boolean]