Updated readme to mention use of JPGraph
Fixed elo calc

The @place var in the SQL query was miscounting, and the $id var went
missing from the php scripts, meaning it looked at the same game
multiple times!
Updated elograph
fixed player.php

Tenhou array is now pre-assigned with "N/A" to prevent errors if the
database has NULL for an entry.

Game history now only shows 4 player games (for now!)