Custom Embed widget in Markdown Editor

[Blocker226]

Hi, as someone who has been using Decap CMS for a portfolio site, I often come across the need to embed items into my posts, such as itch.io's game button or a YouTube video. I'm aware that YouTube video support via widget is coming, but I'd like to be able to extend this to support any set of tags.

I've been working around this issue in Decap CMS via a custom widget, but I think an optional, generic "Custom Embed" component in the markdown editor would be useful to have built-in.

[kyoshino]

I plan to add basic support for custom editor components soon.