Add HISTTIMEFORMAT variable to allow custom history date formatting
It would be nice to have some sort of way to use the timestamps saved by HISTORY_TIMESTAMP. In Bash, I use HISTTIMEFORMAT='%F %T ' and that gives a nicely formatted history with timestamp, like:
188296 2020-10-17 18:42:47 vim .config/ion/initrc
188297 2020-10-17 18:50:26 history