* nuke: use macOS open when GUI enabled

* nuke: use is_mac function to test for macOS

This is consistent with how the imgur plugin does detection.

* Add macOS open command to plugins

* pskill: only execute if input is non-empty

* Added padding for numbers in .nmv

* Add skim as an option in fzopen

* Remove unnecessary eval

Thanks @leovilok!

Co-Authored-By: lvgx <l@vgx.fr>

* Added note about whitespace

Co-authored-by: lvgx <l@vgx.fr>