Include images in documentation in generated content

[tymokvo]

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Hello,

I have been trying to include visual content in library documentation. My use case is that I am working on a project that interfaces heavily with CAD workflows. So, it would be very valuable to be able to save snapshots of diagrams/drawings and include them in documentation that is then built into the static content by fsdocs.

I first asked on the fsharp slack for advice on the topic.

For example:

/// Pi is the ratio of circle's circumference to its diameter.
/// ![remote image](https://www.probability.ca/jeff/writing/pi1.jpg)
///
/// ![local image](images/pi.png)
let pi = 3.14159

Would result in an HTML tag like <img src="{root}content/img/pi.png" /> (or some other path in the output directory) in the documentation for that value.

It would be nice to be able to support embedded HTML, especially for resizing images. But I think supporting markdown images would be a good start if it is not already supported.

I have tried running fsdocs build --saveimages=all flag, but it seems to have no effect. This is possibly due to #683.

---

Looking through the markdown parser, it seems that this syntax should be supported to include an image:

https://github.com/fsprojects/FSharp.Formatting/blob/2efb355823b8311f91a06566c0a3de86037a590d/src/FSharp.Formatting.Markdown/MarkdownParser.fs#L479-L498

And looking through the BuildCommand, it seems that remote and local images should be supported:

https://github.com/fsprojects/FSharp.Formatting/blob/2efb355823b8311f91a06566c0a3de86037a590d/src/fsdocs-tool/BuildCommand.fs#L49-L71

Though, the imageSaverOpt value in processFile seems to only ever be passed into the Literate methods, which is what I assume the linked issue is in reference to.