Support `autosquash` with `fixup!` commits
As a developer, I would like to easily squash commits prefixed by `fixup!`, in order to quickly rebase branches without reordering fixups manually.
This feature is natively supported by `git` with the `--autosquash` option and by `git-cola`.
Current steps to achieve the same goal today:
1. reorder the commits by hand;
1. select `squash` in the commit fix;
1. edit the comment of the main commit to remove the duplicate messages.
Those operations might be very tedious, time consuming and error prone especially when there are a many commits to fix and/or many fixups. Above all when you have to cancel the rebase for some reasons and start again.
With the `autosquash` feature, the same need could easily and quickly be done. It would just require to prefix the commit with the `fixup!` magic comment and let the tool automatically achieve the 3 steps above: reorder, select the `squash` mode and remove the duplicate messages.