[core-workflow] Update from the PyCon language summit

Basically the key things that came out of the language summit are two things. One is that to move over cpython will require matching what we have now, so when a commit lands on the repo that bugs.python.org gets a message and a way to associate an issue with a PR (probably something like detecting "Issue #" in the title of the PR and then making the association on bugs.python.org). Otherwise dealing w/ sys._mercurial/sys._git and updating the devguide are the only requirements. Two, in order to shutdown Rietveld we will need to back up the database of code reviews and dump the review information in some readable format (maybe something as simple as running wget over Rietveld).