ENH GLM add score_obs and score_factor
TST: GLM score_obs add unittests against discrete and OLS
ENH GLM add hessian, eim_factor and oim_factor
ENH: GLM add score_test to model
TST: GLM score_test add test verified with R
REF GLM merge oim_factor, eim_factor into hessian_factor
DOC: GLM docstring for score_obs, hessian and score_test
TST: GLM score_test, add test for gaussian/OLS
Merge pull request #1781 from josef-pkt/glm_score

ENH: Glm add score_obs