Create pkgdown reference index

[Bisaloo]

scoringutils exports a lot of functions and while I was trying to learn more about the package functionality, it was difficult to create mental categories of which function serves which purpose. In this PR, I make these categories explicit by creating a reference index for the pkgdown website.

I can revisit this PR as much as necessary, e.g., by adding a short description for each category. I also see that you are probably in the process of submitting to CRAN so feel free to delay merging this PR as you might not want to introduce extra sources of potential issues at the last minute.

For reference, here is the relevant pkgdown help page where you can see all the options for the reference index: https://pkgdown.r-lib.org/reference/build_reference.html

A screenshot of the output:

[codecov]

Codecov Report

Merging #113 (3c95cf0) into master (c091495) will increase coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #113      +/-   ##
==========================================
+ Coverage   48.74%   48.85%   +0.11%     
==========================================
  Files          18       18              
  Lines        1356     1357       +1     
==========================================
+ Hits          661      663       +2     
+ Misses        695      694       -1     

Impacted Files	Coverage Δ
R/eval_forecasts_helper.R	100.00% <ø> (ø)
R/pairwise-comparisons.R	42.14% <ø> (ø)
R/utils.R	63.49% <ø> (ø)
R/sharpness.R	75.00% <0.00%> (ø)
R/eval_forecasts_continuous_integer.R	69.64% <0.00%> (ø)
R/eval_forecasts_quantile.R	94.05% <0.00%> (+0.05%)	⬆️
R/eval_forecasts.R	66.07% <0.00%> (+0.89%)	⬆️

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[nikosbosse]

This is really nice! So when you build the package it automatically builds a html file with the contents of the package?

[Bisaloo]

Ah yes, sorry, I should have mentioned it. The current page is here. It contains the list of documented functions in scoringutils (even if they're not exported, as long as they're documented). By default, it's a single list but you can group the functions in categories to make discovery easier.

In short, it will not change the package itself, neither its functionality nor its built-in documentation. It will only affect the online documentation available at https://epiforecasts.io/scoringutils/.

[Bisaloo]

And yes, with the change proposed here, the pkgdown.yaml action will automatically build this references/index.html file after each push to the master branch.

[nikosbosse]

sweet! Thanks :)