h_check_fun_formals: Checking Formals of a Function
In 0liver0815/onc-crmpack-test: Object-Oriented Implementation of CRM Designs

This helper function checks whether a given function fun has required or allowed arguments. The argument check is based only on the names of the arguments. No any further logic is verified here.

1	h_check_fun_formals(fun, mandatory = NULL, allowed = NULL)

`fun`	(`function`) a function name whose argument names will be checked.
`mandatory`	(`character` or `NULL`) the names of the arguments which must be present in `fun`. If `mandatory` is specified as `NULL` (default) this requirement is ignored.
`allowed`	(`character` or `NULL`) the names of the arguments which are allowed in `fun`. Names that do not belong to `allowed` are simply not allowed. The `allowed` parameter is independent from the `mandatory`, in a sense that if `mandatory` is specified as a `character` vector, it does not have to be repeated in `allowed`. If `allowed` is specified as `NULL` (default), then it means that there must be no any arguments in `fun` (except these ones which are specified in `mandatory`).