Allow multiple covariates

[drisso]

The user should be able to adjust for other (categorical and continuous) covariates in addition to batch.

[allonw]

I assume that this means allowing any design matrix of technical covariates (maybe with some convenience functions for common cases)? If so, it should be allowed also for the bio covariates.

[drisso]

Yes. It should allow an arbitrary number of covariates to be removed and an arbitrary number of covariates to be preserved.

[drisso]

The plan is to add a single covariate for the moment. To do this:

• [ ] Add the adjust_covariate=c("no", "yes", "force") argument
• [ ] Modify parse_row() and make_design()
• [ ] Modify scone()