Arvados

Background: Most of our users using the Arvados API are doing so through the Python SDK. Showing examples in Python makes the reference documentation more useful to developers who may not have used web APIs before.

At the same time, the Python SDK isn't the only SDK, and we do want the reference documentation to be useful to developers using other SDKs, or even writing their own SDK.

Extend the API reference documentation so there's two version of each example: a Python version and a "plain HTTP" version. Each example offers the reader a way to switch between versions. That choice is remembered and used across all examples.

The system should have room to accommodate other versions in the future but those versions aren't added in this ticket, those are follow-up tickets.