PERF/ENH:  Add discrete to vbench.
PERF/ENH: Add discrete
PERF/TST: Add formula to ols.
BUG: Passed wrong statement for formula.
PERF/TST: Remove failing negative binomial vbench.
BUG: Removing failing discrete benchmarks.
BUG: Remove failing discrete benchmarks.
CLN: Removed unused imports and pandas -> statsmodels.
BUG: Fix typos in ols benchmarks.
CLN: Remove TODO and fix db in .gitignore.