REF rename NegativeBinomial scoreobs -> jac
REF/ENH: generalize sandwich_covariance to work with discrete MLE
TST: Count regression, cluster robust, first tests
BUG: fix missing .shape in sandwich_covariance refactoring
Merge pull request #1225 from josef-pkt/sandwich_mle

REF/ENH generalize sandwich_covariance to work with mle models (discrete)