Combat

* Enhanced error handling for confounded variables

* Updated copyright

* Updated dependency versions

* Corrected a bug preventing the definition of batches with lists of strings

* Corrected typos in the documentation

* Corrected a bug preventing the use of multiple covariates at the same time

* Corrected a bug preventing the use of batch 0 as a reference batch

* pyComBat now exits with an informative message when nans are detected

* Removed soon deprecated functions calls

* Covariates can now be defined by a simple list instead of a model matrix

* Performances enhancement

* Batches can now be defined with non-integers lists (e.g. strings)

* Covariates can now be taken into account for the batch-effects correction through the use of a model matrix

* Corrected a bug forbidding the first batch to be a reference batch

* Added unit testing

* First release