estimate_treat_prob: Estimate probability of receiving each level of treatment
In drord: Doubly-Robust Estimators for Ordinal Outcomes

Estimate probability of receiving each level of treatment

1	estimate_treat_prob(treat, covar, treat_form, return_models)

`treat`	A `numeric` vector containing treatment status. Only values of 0 or 1 are treated as actual treatment levels. Any other value is assumed to encode a value for which the outcome is missing.
`covar`	A `data.frame` containing the covariates to include in the working proportional odds model.
`treat_form`	The right-hand side of a regression formula for the working model of treatment probability as a function of covariates
`return_models`	If `TRUE` the fitted working proportional odds models and treatment probability models are returned.

A list where the first element is estimate of Pr(treat = 1 | covar) for covar equal to inputted values of covar and second element is estimate of Pr(treat = 0 | covar) for covar equal to inputted values of covar