create_sa: A generic sensitivity analysis object
In DARTH-git/dampack: Decision-Analytic Modeling Package

This function is called by make_psa_obj, create_dsa_oneway, and create_dsa_oneway, and checks the structure of each of the arguments before creating an SA object.

create_sa(
  parameters,
  parnames,
  effectiveness,
  strategies,
  cost,
  currency,
  other_outcome
)

`parameters`	a data frame with parameter values for each model run. Each column should represent a different parameter, and each row should represent a simulation (in the same order as `cost` and `effectiveness`)
`parnames`	names for the parameters.
`strategies`	vector with the names of the strategies. Due to requirements in certain uses of this vector, this function uses `make.names` to modify strategy names as necessary. It is strongly suggested that you follow the rules in the `make.names` help page, to avoid unexpected errors.
`cost, effectiveness, other_outcome`	data frames containing data for costs, effectiveness or another outcome (user-defined), respectively. Each simulation should be a row of the data frame, and each strategy should be a column. Naming the columns of the data frames is not necessary, as they will be renamed with the `strategies` vector.
`currency`	symbol for the currency being used (ex. "$", "£")