EX: Updated example for fixed code.
Merge pull request #2115 from jseabold/update-mixedlm-notebook

EX: Updated example for fixed code. [skip ci]
TST: Failing test for AR order select.
BUG: Fix optimizer/model for full_output = 0. Closes #2118.
TST: Expand full_output=0 to all solvers.
REF: None is a Singleton
REF: Refactor so full_output is consistent across models.
REF: Refactor for consistent full_output=0
TST: Test full_output=1
TST: basinhopping not available in all scipy versions.
Merge pull request #2119 from jseabold/fix-2118

BUG: Optimizers broken for full_output = 0.