Add more scoring to pmdarima.arima.AutoARIMA

[iajoiner]

Is your feature request related to a problem? Please describe.

I'm frustrated since I can not use scores other than MAE and MSE to select the best parameters for ARIMA.

Describe the solution you'd like

I would like to enable MAPE, SMAPE as well as custom scoring functions in AutoARIMA and would like to contribute the code.

[tgsmith61591]

Thanks for the willingness to contribute the code! This would be a good feature

[iajoiner]

You’re welcome! Looks like I may only need to change some docstrings.