Add the work-in-progress Bun-based implementation

It doesn't have all the features of the Node-based implementation yet, but it's getting there and there are to-do items in the readme capturing what's missing.

Author: TomasHubelbauer

Block.ts

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+export type Block = {
+  tag: string;
+  meta: string;
+  code: string;
+  path?: string;
+};

demo/javascript-exception/readme.md

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+# JavaScript exception
+
+```javascript
+throw new Error('Hello, world!')
+```

demo/javascript-expression/readme.md

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+# JavaScript expression
+
+```javascript
+'Hello, world!'
+```

demo/shell/readme.md

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+# Shell
+
+```sh
+echo "Hello, world!"
+```
+
+```sh
+>&2 echo "Hello, world!"
+```

demo/stderr-file/.gitignore

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+stderr.txt

demo/stderr-file/readme.md

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+# Standard error stream to a file Hello World!
+
+`stderr.txt`:
+
+```stderr
+Hello, standard error!
+```

demo/stderr/readme.md

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+# Standard error stream Hello World!
+
+```stderr
+Hello, standard error!
+```

demo/stdout-file/.gitignore

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+stdout.txt

demo/stdout-file/readme.md

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+# Standard output stream to a file Hello World!
+
+`stdout.txt`:
+
+```stdout
+Hello, standard output!
+```

demo/stdout/readme.md

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+# Standard output stream Hello World!
+
+```stdout
+Hello, standard output!
+```