Consider moving Dot and PlantUML diagrams inside markdown

[Penaz91]

There are filters like diagram that allow integrating diagrams inside the text of a markdown. This would make easier editing and eventually reduce the footprint of the book.

[Penaz91]

Considering that some graphviz diagrams will have to be rendered using different engines (dot, neato, twopi...), it's not worth trying to include them in the text itself.

It would only end up extending the time it takes to compile the book and make the quality drop, since it would give less stability on rendering than SVG images (which sometimes end up being unstable themselves).