Generate SVG from sequence diagram definitions
Pimp pages with sequence diagrams

Add sequence diagrams using fenced code blocks with a 'sequence-diagram' class

```sequence-diagram
Andrew->China: Says Hello there
Note right of China: China thinks\nabout it
China->Andrew: How are you?
Andrew->China: I am good thanks!
```
Convert one sequence diagram image to new format.

- still needs work in the visual department