geom_textsegment()

[teunbrand]

Hi Alan,

This PR adds the geom_textsegment() and geom_labelsegment() functions, the former originally mentioned in #5 (comment). Due them typically being straight, straight = TRUE is the default for Cartesian coordinates.

In addition, it adds the rd_dots() function to put in #' @eval rd_dots(funname) roxygen documentation. The intended use is for children of GeomTextpath and GeomLabelpath, so we can omit all the static text parameters from the function formals and in the params of the constructor. These typically go through ... and rd_dots() should figure out which ones are in the formals and which get passed through .... Ultimately, this makes it slightly less verbose in our code to include these parameters.

library(ggplot2)
#> Warning: package 'ggplot2' was built under R version 4.1.1
library(geomtextpath)

sleep2 <- reshape(sleep, direction = "wide",
                  idvar = "ID", timevar = "group")

ggplot(sleep2, aes(x = "Drug 1", y = extra.1)) +
  geom_textsegment(
    aes(xend = "Drug 2", yend = extra.2,
        label = paste0("Patient #", ID)),
  )

^{Created on 2021-12-21 by the reprex package (v2.0.1)}