feat: add trashing

[RaafatTurki]

fixes #279

adds the ability to trash with D, trash command and confirmation message are configurable in setup() which is documented as well.

[RaafatTurki]

It's relocated now and much more inspired by fs.remove().
However an issue was brought to my attention, after trashing an item an R refresh is required to update the tree to its correct view.

I've thought I should give the trash process time to execute before doing a lib.refresh_tree() so I've tried doing it in on_exit() to no avail.

I don't have a good image on how nvimtree handles UI updates, I'd like you to take a look
here and here

[kyazdani42]

just missing documentation in help file :)

[kyazdani42]

CI complaining about unused arguments, please remove them if they are unused :)

[RaafatTurki]

done

[kyazdani42]

thanks :)