* Implemented custom user command execution on the following menu events: entry selected, entry accepted, menu canceled, menu error, mode changed, screenshot taken
* fixed different signedness comparison warning and compare unfiltered entry index in selection_changed_user_callback
* track previously selected line in RofiViewState
* added documentation about custom scripts to run on certain actions
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Co-authored-by: Matteo <giomatfois62@yahoo.it>