REF: Get rid of plain assert.
Merge pull request #1336 from jseabold/assert-clnup

REF: Get rid of plain assert.
ENH: Convenience function for order selection by IC
TST: Smoke test arma order selection.
TST: Mark as slow.
ENH: Add new function to __all__
REF: Use import * since __all__ is defined.
DOC: Clarify implementation in the notes.
DOC: Add arma_order_select_ic note to docs and release notes
TST: Add regression test for arima_order_select_ic
ENH: Add min_order to order select results