This function returns all of the possible hector output variables
that can be accessed with fetchvars.
Examples
if (FALSE) { # \dontrun{
ini <- system.file(package = "hector", "input/hector_ssp245.ini")
hc <- newcore(ini)
run(hc)
out <- fetchvars(core = hc, dates = 1900:2100, vars = ALL_VARS())
print(out)
} # }