Add a basic adapter for public Tableau visualizations

[mlncn]

No description provided.

[oscarotero]

Hi. Thanks for your contribution. I just have a couple of changes:

• The Code detector is not correctly implemented. See other examples, like https://github.com/oscarotero/Embed/blob/master/src/Adapters/Gist/Detectors/Code.php
• Please, add a test for this url.

[mlncn]

Thank you! Is a code detector needed? Tableau doesn't return a code (that i can find) so we just build one.

[oscarotero]

Mmm, I think your code is using the v3.x version of Embed, instead of v4.x.

In v4.x, all code detectors must return a EmbedCode instance (no matter if the code is returned by the site or hand-built).

Could you convert this code to v4?