Examples of DOM manipulation with Webassembly

[mireille-raad]

Write an article with examples of DOM manipulation with Webassembly and possibly include those examples in the snippets/official demo.

Mentioned on gitter by @phorward and in RustPython/RustPython#825

[phorward]

Hello, thanks for mentioning. I've already started a test branch for myself here https://github.com/phorward/RustPython/tree/feature/html5-tests, but I think it's first more useful to collect examples.