markdown-preview: Add Markdown preview plugin

[vkareh]

This plugin uses the new right pane in Pluma to display a real-time rendering/preview of a Markdown file. It uses WebKit2 and only relies on core markdown plugins in python.

Needs python3-markdown (or whatever the lib is named in your distro).

Also moved the sourcecodebrowser plugin to the new right panel.

Needs mate-desktop/pluma#718

Markdown Preview plugin:

Source code browser plugin on right side:

[Cyrille37]

Yeah! That's a so great feature 💌

[lukefromdc]

Is there a test file for this? This is one of those things I don't know anything about

[vkareh]

@lukefromdc

Is there a test file for this? This is one of those things I don't know anything about

Try the README.md file in this repo. The .md extension is for Markdown, which is what we generaly use in MATE.

[lukefromdc]

I was unable to build pluma-plugins due to a libpeas issue blocking the build at the word-completion plugin:

                 from pluma-word-completion-plugin.c:29:
/usr/include/libpeas-1.0/libpeas/peas-extension.h:26:10: fatal error: girepository.h: No such file or directory
   26 | #include <girepository.h>
      |          ^~~~~~~~~~~~~~~~

Debian has rebuit libpeas 1.36.0 (1.36.0-8) to declare "breaks" against current eom and eog prior to a certain commit. I don't know much about libpeas but pluma without the plugins package is working fine with libpeas 1.36.0-5

libpeas (1.36.0-8) unstable; urgency=medium

  * Team upload
  * d/control: Increase version of Breaks on eom and pluma.
    Version 1.28.0-1 of each package was uploaded to unstable, so we'll
    need a correspondingly newer upload with the changes for #1118496
    and #1118497.
  * Release to unstable (transition: #1118613) (Closes: #1118363)

libpeas (1.36.0-5)

[vkareh]

@lukefromdc I think your solution for the time being may be to install libgirepository1.0-dev to work around those Debian changes.

Long term I think pluma-plugins (and possibly other packages in MATE) need to explicitly depend on girepository (and handle 1.0 or 2.0 gracefully, or through a build flag)