Prepare the list of priors

`prepare_priors(utility, draws, R)`

- utility
A named list of utility functions. See the examples and the vignette for examples of how to define these correctly for different types of experimental designs.

- draws
The type of draws to use with Bayesian priors. No default is set and must be specified even if you are not creating a Bayesian design. Can be one of "pseudo-random", "mlhs", "standard-halton", "scrambled-halton", "standard-sobol","scrambled-sobol".

- R
An integer giving the number of draws to use. The default is 100.

A list of priors