Support rotate of diagrams

[wimdeblauwe]

If possible, it would be great if diagrams could be rotated 90 degrees. For example, if you include a PlantUML sequence diagram, it can get quite wide. So if it could be rotated, it will be more readable (in the PDF output).

As a workaround, it is possible to have a landscape page, just with the diagram like this:

Some text here at previous page.

[page-layout=landscape]
<<<
Sequence diagram of the flow:

plantuml::mysequencediagram.puml[format=svg]

[page-layout=portrait]
<<<

Rest of the document here.

It is not completely the same of course, rotating the diagram would be better when printing the PDF as all pages remain in portrait.

[pepijnve]

This feels like something the rendering backend could take care of. Especially in PDF (and even in HTML these days), you can specify this type of transformation easily per image.
@mojavelinux do the html5 and/or pdf backends already have some kind of means to specify an affine transform matrix (or something similar) per image?