Time Series Fixes + Deprecation Warning

++++ All Zelig time series models will be deprecated on 1 February 2018 ++++

Bug fixes

• Resolved an issue where odds_ratios standard errors were not correctly
  returned for logit and relogit models. Thanks to @retrography. #302

• Zelig 4 compatability wrappers now work for arima models. Thanks to
  @mbsabath. #280

• Resolved an error when only setx was called with arima models Thanks to
  @mbsabath. #299

• Resolved an error when summary was called after sim for arima models.
  #305

• Resolved an error when sim is used with differenced first-order
  autoregressive models. #307

• arima models return informative error when data is not found. #308

Minor

• Compatibility with testthat 2.0.0

• Documentation updated to correctly reflect that tobit wraps AER::tobit.
  #315

• Package terminology in documentation corrected. #316