====== Options controlling the history ======

''bang_hist''
  * enable '!' history expansion

''append_history''
  * when exiting, append history entries to $HISTFILE, rather than replacing the old file; this is the default

''extended_history''
  * save additional info to $HISTFILE

''hist_ignore_space''
  * if the commandline starts with a whitespace, don't add it to history

''inc_append_history''
  * append every single command to $HISTFILE immediately after hitting ENTER.

''share_history''
  * always import new commands from $HISTFILE (see 'inc_append_history' above)