This is to follow up on how to allow APM vendors to integrate with OpenCensus by having more access to span/spancontext.

1. We will use Google doc for the design discussion.
2. We will pilot in OpenCensus Python. An experimental development branch will be used for the work in OpenCensus Python.
3. Once the work got validated, we will lock the design in opencensus-specs.
4. Once the design got accepted by opencensus-specs, we will merge the Python experimental branch into master, and start the implementation in other languages.
5. This effort should not affect/block the current OpenCensus Python release schedule.