Fixed typo in preview-kitty.

Thanks @Kabouik!

* Added GPG encrypt and decrypt plugins

* Made description more descriptive

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

* preview-tui: simplify, add generic fifo_pager()

I've commented new filetype checks for now, as we need to discuss which ones
should be included by default, keeping in mind that this is supposed to be a
minimal, adaptable plugin.

* preview-tui: preview with man, tar, unzip by default

This is a trial patch to fix the typos

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

* Add -a option to generate a temporary NNN_FIFO

* Add documentation for -a option

* plugins/README.md: promote the use of -a

This obsoletes the global FIFO unlink trick, so I remove mentions of it.
@jarun update:

Polish -a

* preview-kitty: async version

The plugin now aborts slow file viewers.

* preview-kitty: use text mode preview for SVG

* Allow launching plugins with Alt + plugin's key

* Fix Alt key in filter/prompts modes

* Fix handling Alt key in nextsel()

In filter mode: run the associated plugin.
In prompt mode: just throw out the Alt+key input.
In nextsel(): differentiate Alt+key and Esc

Pass "master" as first argument to the script.

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

As reported by @toddyamakawa

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