Introduce a Configurer trait

Rename `get_history` to `history_mut`
Rename `get_history_const` to `history`
Replace `set_completer` by `set_helper`

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this argument is passed by reference, but would be more efficient if passed by value

Add maintenance badge [ci skip]

And reintroduce `set_completer`.

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We must redraw the line with the original prompt
when the command used to validate/exit the loop is a movement.