Add cap argument

[grantmcdermott]

Closes #576

Note: I settled on the shorter cap (versus caption) argument to better mirror sub, lab etc.

MWE

pkgload::load_all("~/Documents/Projects/tinyplot")
#> ℹ Loading tinyplot
tinyplot(Sepal.Length ~ Petal.Length | Species, data = iris,
         main = "Some flowers",
         sub = "The iris dataset",
         cap = "Source: Anderson (1935)",        
         theme = "clean")

Customization:

tinytheme("clean", col.cap = "grey50", adj.cap = 0)
tinyplot(Sepal.Length ~ Petal.Length | Species, data = iris,
         main = "Some flowers",
         sub = "The iris dataset",
         cap = "Source: Anderson (1935)")

One caveat is that sub and cap are effectively substitutes for non-dynamic plots. But I've been careful to document this.

tinytheme()
tinyplot(Sepal.Length ~ Petal.Length, data = iris,
        main = "`sub` and `cap` overlap for default theme",
        sub = "Subtitle", cap = "Caption")

^{Created on 2026-05-20 with reprex v2.1.1}

[grantmcdermott]

Sorry to tag for a review again @zeileis and @vincentarelbundock. But this is the penultimate design-based change that I want to roll into the upcoming v0.7.0 release. (The final one will be a reworking of some of our existing themes, plus adding some new ones.)

So I'd appreciate you just casting a quick eye over the API and giving a thumbs up if you approve.

[vincentarelbundock]

Looks good to me! Nice that you added all the tpar() to control it too.