articles/configuration-api-refactoring

following the discussion in the requirement repo, this is the first draft of the whole configuration documentation refactoring. Currently is a "split" of the old documents into doc sections.

Misses a couple of things already discussed, but not yet finalized, my proposal is to:
* review;
* merge;
* iterate to add missing parts (I already have a list of issues to open)

/cc @dannycohen @SimonCropp