create_model: Create regression model
In timwilson/soty: Calculate Performance Points For Various Archery Rounds

Fit a linear or exponential model to the trimmed CDF of archery scores.

1	create_model(results, perfect_score, score_col, mode = "exp")

`results`	A dataframe containing archery scores.
`perfect_score`	The maximum number of points possible for the specific archery round
`score_col`	The name of the column in the data frame that contains the scores
`mode`	The type of function ("exp" or "linear") to fit to the results data.