falls back to previous behavior if $VISUAL is not set ($EDITOR then vi)

* 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

- Add a native vector icon for Haiku (it hasn't been Haiku-ified yet however)
- Add a rdef file (specifies application metadata)
- Add clipboard support, notififcation support, and basic nuke support
- Fix support for fortunes on Haiku ("-s" option is not available on Haiku)
- Cleanup Haiku recipe

* added support webp format

* update nuke plugin with support webp format

This is a trial patch to fix the typos

Signed-off-by: SZ Lin (林上智) <szlin@debian.org>

* Add nvim as a diff tool for getplugs plugin

* Comment out `is_cmd_exists()`

* Add nvim diff tool for diffs plugin

* Add $EDITOR to nuke plugin for editing/reading text file format

* Modify diff command to fix CircleCI failures

* Fix getplugs prompt

* Allow nuke to use custom $PAGER

See https://kristaps.bsd.lv/lowdown/

Replaces the following environment variables:
- NNN_USE_EDITOR
- NNN_IDLE_TIMEOUT