New WIP DUB documentation

[WebFreak001]

Hi all, I'm currently working on new revamped DUB documentation, 
check it out if you want, it currently contains most old 
documentation plus a big bunch of new documentation:

https://docs.webfreak.org/

Repository: https://github.com/WebFreak001/dub-docs-v2

Instead of being based on diet templates and needing to be 
compiled using `dmd` and build all of vibe.d, it now uses 
[mkdocs](https://www.mkdocs.org/) with a customized [mkdocs 
material theme](https://squidfunk.github.io/mkdocs-material/), so 
now the documentation is Markdown based, which should be more 
familiar to a lot of people + it has a great offline search index 
and a bunch of interactive elements, that also work without JS.

The dub.json and dub.sdl documentation is now merged on the same 
page, where you can simply swap between them whenever you like. 
If you have JS enabled it will also sync it across the entire 
page and persist across page loads.

Writing the docs is really quite easy, you can have it locally be 
served by first installing the dependencies using

```
pip install -r requirements.txt
```

and then when working on it running

```
mkdocs serve
```

to have auto-updating docs in the browser. (auto refresh whenever 
you change anything)

So if you find any typos or want to complete the docs, feel free 
to open a PR on https://github.com/WebFreak001/dub-docs-v2

I plan to have easily discoverable edit links linked on the page 
soon too, which should theoretically just be a simple mkdocs 
configuration thing that's probably already implemented.

Someone from the community has already contributed a dark theme 
to it. :)

[![new dub documentation preview 
screenshot](https://wfr.moe/f6fgF7.png)](https://docs.webfreak.org)