Uses `NNN_FIFO`, minimal dependencies.

Co-authored-by: Todd Yamakawa <todd.yamakawa@arm.com>

Co-authored-by: Todd Yamakawa <todd.yamakawa@arm.com>

* Add a tabbed/xembed based file previewer plugin

This plugin is written in bash, because job control is not well
specified in POSIX sh (`jobs` can return anything).

We use `tabbed` [1] as a xembed [2] host, to have a single window
owning each previewer window.

Uses mpv, sxiv, zathura, and the nuke plugin.

[1]: http://tools.suckless.org/tabbed/
[2]: https://specifications.freedesktop.org/xembed-spec/xembed-spec-latest.html

* tabbed-preview: prevent focus steal with xdotool

* preview-tabbed: tabs->4 spaces

* preview-tabbed: add focus prevention timeout

* Add an option to print hovered files to a FIFO

This adds an env variable, `NNN_FIFO`, that can be set to a path that
`nnn` will open/create as a FIFO, and where every hovered file's path is
printed. This allows creating external perview/quick open plugins, ...

It can be compiled out with the make variable `O_NOFIFO`.

* Check filename ptr instead of full path (for FIFO)

* Add documentation to use NNN_FIFO in plugins

* Fix path sent to FIFO in empty dirs

Support `$_Z_DATA` environment variable per z's documentation dcd5541e7d/z.1 (L78).
`$_Z_DATA` allows changing the default location of the z database file.

* Add nbak plugin to backup all nnn config

* nbak: check cd, quote env

* nbak: print backup file name

* nbak: add --show option, to show shell config

* nbak: fix shellcheck warning

'type' is POSIX complient, AND we check that we're actually running
bash, but shellcheck can't understand this...
Then '-o' is POSIX complient too, but shellcheck thinks it's "not well defined".

* nbak: variable renames, archive hierarchy changes

* nbak: fix variable expansion

* nbak: remove --show option

* nbak: call interactive bash/zsh to get fun/aliases

* Add nbak entry in plugins/README.md

* nbak: change archive hierarchy

* plugins/README.md: make nbak description shorter

* 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>

* 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/

* Added fzfz plugin

* Fixed shellcheck errors

* Fixed copy/paste error

* Added support for fzy, also renamed plugin since it's not specific to fzf anymore

* Refactored code

* Clean spillovers (jarun)

* Added fzfz plugin

* Fixed shellcheck errors

* Fixed copy/paste error

This plugin is based on .cbcp and does basically the reverse operation.
It copies system clipboard newline-separated file list to selection.

* Fix empty printf, change separator for sed

* Added missing quotes

* Added (almost) POSIX compliant batch rename script

* Not fully

* Added selection/current prompt