Focus on:
Public API and SPI Review

How can I implement a custom Dataformat?

How can I configure Spin in the process engine?
When would I use which artifact?
e.g. if I want to configure Jackson from outside, use Jackson annotations etc. I should use spin-core. This has to be documented in the platform docs as well as spin docs on github.

related forum post:
https://groups.google.com/forum/#!topic/camunda-bpm-users/7lmaGZKk9K4