ENH: hc3 cov_type for GMM, GMMIVNonlinear

[josef-pkt]

this article has pseudo-hatmatrix for small sample corrections for HC2, HC3, ...

moment condition z (y - g(x, beta)) i.e. nonlinear IV, but not for generic nonlinear GMM

Lin, Eric S., and Ta-Sheng Chou. “Finite-Sample Refinement of GMM Approach to Nonlinear Models under Heteroskedasticity of Unknown Form.” Econometric Reviews 37, no. 1 (January 2, 2018): 1–28. https://doi.org/10.1080/07474938.2014.999499.

I did not find any HC3 equivalent for generic GMM, and nothing for more general non-gaussian MLE.
(Poisson, GLM use the IRLS, WLS hatmatrix)