Feature request: coef method for margins objects

[tzoltak]

[x] a suggested code or documentation change, improvement to the code, or feature request

If a simple coef() method for margins objects would be added to the package, it will enable for example easy computation of AMEs on multiply imputed datasets using package mitools. I think it may look as simply as:

#' @export
coef.margins <- function(object, ...) {
  summary(object)$AME
}