Building custom library package with dub

[alex1974 via Digitalmars-d-learn]

I want to build a custom library with useful extensions to 
phobos. They should be named like:

extensions.regex
extensions.path
extensions.files
...
Some libraries, like extensions.files contain several files (e.g 
files.d, filesexceptions.d)

Analog to phobos I would like to import them like
import extensions.files: temporary;

What would be the best approach for the folder layout and dub?
I guess subPackages, but I can't get them to compile and link 
properly.

Thanks for the help