Move SDLang-D to dlang-community

[WebFreak001]

upstream issue: dlang-community/SDLang-D#75

@s-ludwig @Geod24 since sdlang-d is vendored in dub, what do you think of this? I think the original author might not be available anymore, so we would need to fork it here and rename it.

[s-ludwig]

What I would consider instead would be to switch to sdlite. I didn't push for that so far simply because there really was no reason to put any effort into it, but if we'd ever run into issues with the parser I think that makes more sense.

The reasons speaking for sdlite:

• Considerably faster (> 10x)
• No dependencies, small code base
• Used regularly in production
• The serialization library might be interesting

The existing code should be trivial to port with some mechanical adjustments to account for the differing AST API.

[WebFreak001]

sounds good to me to use instead as well. I wanted to try making a formatter for SDLang-D so I needed to know where tokens end, but that wasn't implemented. So I have my PR for that open there right now, but with sdlite it looks like that's already possibly out of the box.

The MIT license is also a bit more permissive than zlib/libpng that SDLang-D has I think.