VERSION 1 works with django 1.6
VERSION 2 works with django 2.0
VERSION 3 works with django 2.0

App also tracks other statistics like:
    win - loss records
    win streaks
    points against / points for averages

Separate stats available for
    current year and all-time.

Charts of player ratings over time,
    if chart.js installed.

Ability to create multiple separate leagues.

+ App is written to be installed as "pingpong"
        and not as "pingpong_rating"

+ As games are added, some additional database indexes may be required.

    When I got to ~2000 ratings in pingpong_rating I needed to add this:
        CREATE INDEX i_pingpong_rating_dt ON pingpong_rating (datetime);

+ See notes in models.py for upgrading from an earlier version