Rename pairwise comparisons

[nikosbosse]

Description

As discussed in #638, this PR

• renames add_pairwise_comparison() to add_relative_skill()
• renames pairwise_comparison() to get_pairwise_comparisons()
• renames plot_pairwise_comparison() to plot_pairwise_comparisons() which is a breaking change I'm sure people will love...
• updates tests, docs and the news file

The rationale for this change is this:

• add_relative_skil() is a bit more descriptive than add_pairwise_comparison() in terms of what it does
• Naming it differently from get_pairwise_comparisons() would make it clear that these are two different workflows with two different purposes (one mainly for plotting, the other for computing scores).
• The name get_pairwise_comparisons() would make the naming of the function more in line with the other get_-functions
• I'd still call it get_pairwise_comparisons() rather than get_relative_skill() because the main thing this function is meant to give you according to our updated workflow is the (visualisation of) mean score ratios (see below)
• The change from plot_pairwise_comparison() to plot_pairwise_comparisons() is a bit stupid. But get_pairwise_comparisons() feels more appropriate than get_pairwise_comparison() and the get_ and the plot_ function should be consistent. We could do aliases? Or stick with the singular after all.

Visualisation of mean score ratios:

Checklist

• [x] My PR is based on a package issue and I have explicitly linked it.
• [x] I have included the target issue or issues in the PR title as follows: issue-number: PR title
• [x] I have tested my changes locally.
• [x] I have added or updated unit tests where necessary.
• [x] I have updated the documentation if required.
• [x] I have built the package locally and run rebuilt docs using roxygen2.
• [x] My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
• [x] I have added a news item linked to this PR.
• [ ] I have reviewed CI checks for this PR and addressed them as far as I am able.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.27%. Comparing base (0982955) to head (004b1f3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #722 +/- ## ======================================= Coverage 95.27% 95.27% ======================================= Files 21 21 Lines 1630 1630 ======================================= Hits 1553 1553 Misses 77 77 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[seabbs]

plot_pairwise_comparisons()

For this little one shall we just chuck in an alias? It seems a bit cruel! Or shall we just be cruel?

[nikosbosse]

Maybe we should just be cruel? I don't know, the downside to aliases that I see is that they clutter the docs and the autocomplete dropdown

[nikosbosse]

Dear future user, if you're reading this and are upset: we apologise for our cruelty. Please blame it on me and only me. I think the change is a bit annoying, but you're code is going to break anyways, regardless of whether we keep the s or not. So we might as well break everything hard this time.. But happy to open an issue if we think it's useful.