[d] support for dub

[prabhu]

The package metadata could be defined in .sdl or .json format. .selections.json could be considered a lock file.

https://github.com/dlang-community/grpc-d/blob/master/dub.sdl
https://github.com/dlang-community/grpc-d/blob/master/dub.selections.json

https://github.com/dlang-community/D-Scanner/blob/master/dub.json
https://github.com/dlang-community/D-Scanner/blob/master/dub.selections.json

Bonus

Occurrence evidence can be constructed using D-Scanner's ast json dump

https://github.com/dlang-community/D-Scanner#ast-dump