(feature request) support for images and mermaid diagrams

[waynehsmith]

While working in plans, I find it useful to create both images (PNG typically) or mermaid diagrams as part of the documentation. These can be embedded in the plan or stored in particular project folders.

It would be useful to have plannotator render these documents/diagrams in line when they are in the plan or link to a renderer via the web server.

Currently the relative folders do not appear in the navigation panel on the left so they are not reachable.

[backnotprop]

Hey, can you give me an example markdown? Markdown and images do render in plans currently.

But maybe there's a specific link style I need to support better.