Add plot_compare

[aloctavodia]

closes #76

There are two major points I want to discuss for this PR (or we can split the discussion into more than one PR).

• Is this the correct approach to implement this plot? I mean I am following the proper "new arviz logic"?
• Modifications relative to the legacy plot_compare

about the second point I would like to simplify the plot and only show the ELPD point estimates + SE. Then we will get rid of the arguments insample_dev, plot_standard_error, plot_ic_diff, order_by_rank, legend. The main reason for this is that these are the most useful elements for the plot and this is how most people use and interpret this plot (including the equivalent plot in the Stan world).

I also would like to add two new arguments (already in the docstring), that I think could help make the plot easier to interpret.

• similar_band : If True, a band is drawn to indicate models with similar predictive performance to the best model. (essentially 4 units from the point estimate of the best model) see figure below. I think this should be True by default
• relative_scale : If True scale the ELPD values relative to the best model, so best model will be 0 and all the rest will be below 0 in the log-scale. Not sure if this should be true or false.

Update

This is how it looks like now in

matplotlib

plotly (the band is missing from plotly, not sure why yet)

bokeh

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.29412% with 10 lines in your changes missing coverage. Please review.

Project coverage is 84.71%. Comparing base (60aac9a) to head (6742f7a). Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/arviz_plots/plots/compareplot.py	90.32%	6 Missing :warning:
src/arviz_plots/plot_collection.py	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #77 +/- ## ========================================== + Coverage 83.84% 84.71% +0.86% ========================================== Files 20 21 +1 Lines 2229 2336 +107 ========================================== + Hits 1869 1979 +110 + Misses 360 357 -3 ```

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[OriolAbril]

I really like the proposed changes. Completely agree on similar_band=True as default, not sure about relative, it is true we don't care about the absolute value, but I expect people to worry about the best one being exactly 0. We could try having it on and if we see people reporting back and getting confused we can turn it off