David Thaler

After the update to forecast 6.2, there is one test failing on tsoutliers in test_wrappers.

Functions `accuracy`, `sindexf` and `seasadj` currently only take R objects. Look at `plots.plot_forecast` for ideas about how to get them to take both.

Functions holt and hw expose the damped parameter, but the option of setting phi is not available. If we can't access phi, then maybe damped should not be exposed.

We now have a data folder and io.py, so use that.