REF: Use fixed params in test. Closes #910.
Merge pull request #1706 from jseabold/fix-test-ar

REF: Use fixed params in test. Closes #910.
Merge pull request #1714 from josef-pkt/fit_constrained

ENH: fit_constrained for Poisson and GLM, and standalone
BLD: Made build extensions more flexible
REF: Replaced del with remove
FIX: Replaced remove with pop