[Feature Request] Support PGN code blocks

[purefan]

Hello!

I dont know if this is out of scope for your plugin but here it goes... Chess games are written in a standard format called PGN (portable game notation). We have a fantastic open source PGN viewer provided by lichess here:
https://github.com/lichess-org/pgn-viewer#usage

My request is to take a block of pgn code and append the viewer after, for example:

```pgn
1. e4 c5 2. Nf3 d6
` `` 

would trigger something like:

import LichessPgnViewer from 'lichess-pgn-viewer';

LichessPgnViewer(newDomElement, { pgn: '1. e4 c5 2. Nf3 d6' });

• Your plugin needs to create newDomElement right after the pgn block.
• The default settings for the chess viewer are fine
• The idea is to have a chess board after the PGN where we can move back and forth to follow the game
• The viewer implements all the functionality to browse the game. You dont have to implement any logic to flip the board, go to the next move or anything like that
• The viewer supports another string called FEN, that is to display a specific position. I would say that is not needed right now, but if you feel like it maybe a block code named FEN/fen would do it, in that case instead of the second argument having the property pgn it would be fen

Much obliged :)

[CalebJohn]

Very cool suggestion! I wasn't familiar with PGN. I would say that it's out of scope of this plugin. Rich markdown aims to improve the markdown viewing experience of the base Joplin (without plugins). PGN viewing is not a Joplin feature, and thus not something I intend to explicitly support in this plugin. That said, it should be possible to create what you suggest as a separate plugin, rich markdown doesn't do anything too special that can't be done in other plugins.

That said, eventually I would like to support any renderable item from the viewer to be shown inline in the markdown view. So if someone ever creates a PGN renderer for Joplin, it might be brought in to this plugin :)