Create a `slim_create_sim()` function to automatically convert a `slimr_script` to a function.

[rdinnager]

This would take a slimr_script and return a function that runs the simulation for a batch of parameters. Parameters would be automatically determined from slimr_template() and slimr_inline() calls. Should have an option to vectorize and/or parallelize the simulation, and whether to create individual arguments for parameters or to accept a list of parameters.