Support diagrams as code with Kroki

[kazk]

Support all the diagrams as code with https://kroki.io/. They provide a free service, but we can self-host if necessary.

This can be in a separate package @codewars/marked-kroki.

The implementation is as simple as:

import { deflate } from 'pako';

const kroki = (base = 'https://kroki.io') => {
  if (base.endsWith('/')) base = base.slice(0, -1);
  return {
    code(code, language) {
      // TODO Support options. `{name} ?foo=1&bar=2`
      // TODO Support captions and alt text
      if (diagramTypes.has(language)) {
        const u8 = deflate(code, { level: 6 });
        const data = base64(String.fromCharCode.apply(null, u8));
        return `<img src="${base}/${language}/svg/${data}">`;
      }
      return false;
    }
  };
};

// Base64 URL safe
const base64 = (s) => btoa(s).replace(/\//g, '_').replace(/\+/g, '-');
// All supported types
const diagramTypes = new Set([
  'graphviz',
  'blockdiag', 'seqdiag', 'actdiag', 'nwdiag', 'packetdiag', 'rackdiag',
  'mermaid', 'ditaa', 'svgbob', 'erd',
  'plantuml', 'c4plantuml', 'nomnoml', 'umlet',
  'vega', 'vegalite',
  'bpmn', 'wavedrom', 'bytefield',
  'excalidraw', 'pikchr', 'structurizr',
]);

import marked from 'marked';
marked.use({ renderer: kroki() });

Input:

```graphviz
digraph G {Hello->World}
```

Output:

<img src="https://kroki.io/graphviz/svg/eJxLyUwvSizIUHBXqPZIzcnJ17ULzy_KSakFAGxACMY=">

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