Extensible dub

[simendsjo]

This is just a thought and might not be a good idea.

Dub has quite some special knowledge, like vibe.d, mono-d, visual-d and rdmd.
This makes it a very handy tool, but it also requires every tool to be added in dub directly.

My thought is to forward these to special binaries; dub-build-* and dub-init-*. This way you can easily extend dub for custom libraries/projects without touching dub itself.
dub-init-monod would thus create a mono-d project etc.

[ghost]

Would definitely be a very nice feature to add. I'd say the init wouldn't even require a binary, a simple JSON would be able to say what to do. (It's just a default set of files with a default template and some default settings anyways)

[WebFreak001]

moved into #2210