BUG: fix predict (was refactoring victim)
ENH: GMM fitgmm allow choice of optimizer
REF: gmm, partway through refactoring
ENH: first try at CU-GMM
REF: use pinv for weight matrix in fititer
BUG/REF: gmm cleanup, with unittests,  fititer compares to Stata
REF: gmm cov use ddof=0 as default, more options, OLS test case
BUG/TST: IV2SLS fix df_resid ("small"), plus unit tests
TST: IV2SLS add df_model, more unit test
ENH/BUG: add IVRegressionResults, fix fvalue, see #1104
REF/BUG: move spec_hausman to results class, fix it
ENH: IVRegressionResults add summary
REF/ENH GMM, IVGMM: add summary, partial cleanup weights/inv_weights
REF/TST trying to replicate ivreg2, bse in final iteration?
TST: compare with Stata oneway, twoway, oneway still does something different
ENH: add HAC for weightmatrix, fix arguments, add compare_j (untested)
BLD: add GMM test dta to setup.py (file should be moved)
BLD: try again, add test data file to manifest.in
TST: add (left out) results file
REF/BUG: add `disp` option, fix missing nobs