simplify syntax

[glensc]

instead inventing new blocks, use the code fence language:

$$
    x = {-b \pm \sqrt{b^2-4ac} \over 2a}.
$$

    ```math
        x = {-b \pm \sqrt{b^2-4ac} \over 2a}.

%% sequenceDiagram participant Alice participant Bob Alice->>John: Hello John, how are you? loop Healthcheck John->>John: Fight against hypochondria end Note right of John: Rational thoughts
prevail... John-->>Alice: Great! John->>Bob: How about you? Bob-->>John: Jolly good! %%

```mermaid
sequenceDiagram
    participant Alice
    participant Bob
    Alice->>John: Hello John, how are you?
    loop Healthcheck
        John->>John: Fight against hypochondria
    end
    Note right of John: Rational thoughts<br/>prevail...
    John-->>Alice: Great!
    John->>Bob: How about you?
    Bob-->>John: Jolly good!
```

[BenjaminHoegh]

I do correctly working on change mermaid support to use the example you given. When it comes to LaTeX I will soon update it to use MathJax standard