Slight rework of origin regress.  Results now contain llf_el.
Minor documentation fix
Added tests to ElOriginRegress
For some reason the actual tests didn't get commited.
Merge pull request #787 from j-grana6/origintests

TST: Add tests for Empirical Likelihood Origin Regression
ENH: Working NBin with more loglike choices
ENH: keep full loglik in SM
ENH: removed traces of nbp
ENH: nbin scoreobs
ENH: nbin docstring nb2 vs nb1 vs geom
ENH: reverting change on exog local shortcut in hessian
ENH: NBin -> NegativeBinomial
ENH: nbin pep8
TST: nbin tests
ENH: NegativeBinomial predict
ENH: NBin pickle test
TST: NBin crosscheck R results
ENH: NBin formulas
DOC: NegativeBinomial example
TST: fittedvalues