Document readline in more detail in man/empire.6.
Make @history_file local to main().
main() silently truncates the home directory name to 1000 characters
when constructing the history file name; mark FIXME.
Set @rl_already_prompted just once.
Write history file on unsuccessful exit, too.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>