process_qs: Process the desired sample sizes for 'optimize_controls()'
In natstrat: Obtain Unweighted Natural Strata that Balance Many Covariates

Processes the inputs to optimize_controls() to formulate sample size constraints.

1	process_qs(ratio, q_s, n_s, treated, k, group, st_vals, stratios)

`ratio`	a numeric or vector specifying the desired ratio of controls to 'treated' in each stratum. If there is one control group and all treated units should be included, this can be a numeric. Otherwise, this should be a vector with one entry per treatment group, in the same order as the levels of `z`, including the treated level. If `NULL`, `q_s` should be specified.
`q_s`	a named vector or matrix indicating how many units are to be selected from each stratum. If there is one control group and all treated units are desired, this can be a vector; otherwise, this should have one row per treatment group, where the order of the rows matches the order of the levels of `z`, including the treated level. If `NULL`, `ratio` should be specified. If both are specified, `q_s` will take priority. Typically, if the desired ratio is not feasible for every stratum, `q_s` should be generated using `generate_qs()`.
`treated`	which treatment value should be considered the treated units. This must be one of the values of `z`.