Makes a palette file available by name, so it can be used anywhere a built-in
palette name is accepted. The registration lasts for the session only; to make
it permanent, call this from .Rprofile or pass file = explicitly.
Examples
p <- energypal_create(c(Coal = "#2C2C2C", Solar = "#FFA500"), name = "mine")
f <- tempfile(fileext = ".yml")
energypal_write(p, f)
energypal_register("mine", f)
energypal("mine")
#> Coal Solar
#> "#2C2C2C" "#FFA500"
