Update to [mermaid
v12](https://github.com/mermaid-js/mermaid/releases#release-mermaid@12.0.0),
ELK is now the default layout so the plugin and all supporting code is
gone.
Layout switching to previous `dagre` layout via frontmatter works as
expected. Diagrams use the new `neo` default look which renders them
slightly different (smaller boxes) then the `classic` look that was
default in v11.
The `neo` look got some tweaks to remove shadows and gradient to look
better. Also did some related refactors and mermaid dragging now works
on touch devices too.
silverwind
2b10f77e42