ENH: Make sure mle returns attach to results.
Merge pull request #1367 from jseabold/ar-mle-settings

ENH: Make sure mle returns attach to results.
STY: Pep 8 cleanup
Merge pull request #1368 from jseabold/model-pep8

STY: Pep 8 cleanup
TST: Add tests for failing ARMA(0,0) case.
ENH: Add support for ARMA(0,0) models
Merge pull request #1370 from statsmodels/arima-order-0-0

ENH: Support ARMA(0,0) models.