Performs the Membership Method: Retrieve a member’s listings
using the "query" string provided - should be the "Member/{member_id}/Listings.xml" part of the url. It shouldn't include "http://api.trademe.co.nz/v1/".
public Listings MemberListings(string query) { if (_membership == null) { _membership = new MembershipMethods(_connection); } return _membership.MemberListings(query); }