cli-tools: Parse markdown and generate svg files (embed in markdown?)

[gebv]

Search blocks, parse and insert after found img blocks with svg code with not visible markers
Redraw - find markers, removing and added new
Container with white background. Add dark mode support in future versions.

[gebv]

parse fenced code blocks

```pikchr <figurename>
text "some text"
box "some box"
```

generate and save to disk svg on the path %workspace%/media/pikchr-svg-diagrams/<figurename>.svg