PSA: ArviZ 1.0 released with multiple breaking changes

[OriolAbril]

Please see the migration guide if you are getting errors after upgrading ArviZ.

Highlights of breaking changes:

• InferenceData object no longer exists, we now use xarray.DataTree: https://python.arviz.org/en/stable/user_guide/migration_guide.html#datatree
• Several plots have been renamed, including plot_posterior and plot_trace: https://python.arviz.org/en/stable/user_guide/migration_guide.html#plotting-function-inventory
• Plotting functions now return PlotCollection objects: https://python.arviz.org/en/stable/user_guide/migration_guide.html#what-to-expect-from-the-new-plotting-functions
• waic is no longer available as a function nor model comparison method: https://python.arviz.org/en/stable/user_guide/migration_guide.html#model-comparison