Override from_formula so that extra array args can be passed by name
Test maintenance
BUG/ENH: WLS generic robust cov_type didn't use whitened, see #1896
enable tests
TST: commented out cases in tests
Merge pull request #1989 from josef-pkt/wls_covtype

BUG/ENH: WLS generic robust cov_type didn't use whitened,
Fix exception when no variables are selected
Uncomment test that was inadvertently left commented out
Add assert to test for empty model
Add exposure to GEE, allow offset and exposure to be passed to from_formula
Added test for prediction
Add exposure argument to predict
TST: GEE predict add test case with exog in predict
Merge pull request #1998 from josef-pkt/lasso_emptymodel_1955_rebased

ENH Lasso emptymodel rebased closes #1955
Merge pull request #1999 from josef-pkt/gee_offset_exposure_1994_rebased

Gee offset exposure rebased closes #1994 closes #1991
BLD: let setuptools/pip handle dependencies that are not installed at all.

Closes gh-1897.  See scipy commit 8e7ee0c4b for a similar change that has
worked well.
BLD: use setup/install_requires only if setuptools is installed.
BLD: fix issue with version strings reported by @cel4 in gh-1897.

[ci skip]
Merge pull request #2000 from jseabold/build-deps

BLD: Let pip/setuptools handle dependencies that aren't installed at all.
BLD: Do not generate cython on clean. Closes #1852.
Merge pull request #2006 from jseabold/fix-cythonize

BLD: Do not generate cython on clean. Closes #1852.