Deduplicate history like the fish shell. So for example
entering "cmd 1" then "cmd 2" then "cmd 3" then "cmd 1"
would result in a history of
[cmd 2][cmd 3][cmd 1]
instead of
[cmd 1][cmd 2][cmd 3][cmd 1]
Adds a function `history_add` to replace directly adding to history.
Adds an option `history_dedup` to activate the deduplication.
Defaults to on.
Christoph Heinrich
445a3561d3