*.xy file is now a simple list:

• column 1 is residue type and number for the 1-st residue in a contact
• column 2 is the x coordinate for this contact on the graph
• column 3 is residue type and number for the 2nd residue in a contact
• column 4 is the y coordinate for this contact on the graph
• column 5 is structure number (1 or 2)