Added missing offset to starting value calculation
Rename eta to lin_pred
Docstring edits
Close second part of issue #1720
Rename Y as endog
Handle maxiter=0 as a special case
Added _offset_exposure to _data_attr (but still fails in test_shrink_pickle)
Increase pickle size limit (was failing on GLM)
Break early in IRLS if convergence is detected
Merge pull request #1821 from josef-pkt/glm-maint_1734_rebased

REF Glm maint  rebased closes #1734 (PR)  closes #1728