gd_predict_matches: Goal Difference Model Predict Matches
In neilcuz/panenkar: Panenkar

Predict matches using the basic goal difference rating model

1	gd_predict_matches(match_rating, fit)

`match_rating`	defined as the home_rating - away_rating, where a teams rating is exp weighted average of previous matches goal difference see `gd_calc_rating`
`fit`	fitted probit model using clm, either results ~ match_rating or over_under_2_5 (etc) ~ match_rating
`historic_results`	results to be used for the fitting the model
`market`	see `gd_simulate_matches`
`over_under_goals`	see `gd_simulate_matches`