This PR aims to fix #18.

Briefly, when show.legend = TRUE, the layer is displayed in a legend regardless of whether it has any mapped aesthetics. This caused the geom_hdr_rug()'s key to show up in the alpha guide, despite not mapping alpha. The fix is to set show.legend = NA, which is the default in most layers.

devtools::load_all("~/packages/ggdensity/")
#> ℹ Loading ggdensity
#> Loading required package: ggplot2

ggplot(cars, aes(speed, dist)) +
  geom_hdr() +
  geom_point(color = "red") +
  geom_hdr_rug(aes(fill = after_stat(probs)), length = unit(.2, "cm"), alpha = 1) +
  scale_fill_viridis_d(option = "magma", begin = .8, end = 0)

^{Created on 2024-08-28 with reprex v2.1.1}