Refine DDD mapping into Clojure

[ascho]

Hi! My goal was to investigate how DDD ideas are projected into Clojure programming language and i found your codebase. During investigation i've made changes which imho clarify the exact mapping of DDD into Clojure:

• slightly decrease number of used concepts preserving original approach of distinguishing between events and their application
• core logic assembled in domain services, domain model was distilled to pure specs checking structure and invariants defined upon it
• if keyword intersects module boundary then use only namespace qualified keywords in that case

Pull request is rather large, i decided that there is no sense to make smaller steps without having coherent picture of the final result.

[didibus]

Cool, I'll have a look at it when I have time. It might take me a week to get to it though.