BUG: Ensure 2d for conformability. Closes #1076.
TST: Test ARMAX prediction with 1d exog.
DOC: Clear up requirements for ARMAX prediction.
BUG: Make sure to distinguish 1d row vs 1d obs in predict
Merge pull request #1077 from jseabold/fix-armax-predict

BUG: Allow 1d exog in ARMAX forecasting.