Added: support for binary and count outcomes via generalized estimating equations
Added: Augmented inverse probability weighted (AIPW) estimator to main function via id_form = "DR"
Improved: Expanded simulation function to allow for binary and count outcomes, stratified clustered sampling, and increased parameters to specify the true propensity, selection, and outcome models.
Updated: Main function to be faster for larger sample sizes. Separated pieces of estimation workflow into helper functions (helpers.R) for better compartmentalization.