Currently response return values have to be written twice, once in
the docs and once in zulip.yaml. Create a markdown extension so
that the return values in api docs are rendered using content from
zulip.yaml
Add function in openapi.py to access endpoint descriptions written
in zulip.yaml. Use this function for creating a markdown extension
for rendering endpoint descriptions written in zulip.yaml.
We use this extension for a single endpoint to get test coverage.
Openapi had descriptive response codes for endpoints with multiple
responses for same response code. But this does not fall in line
with openapi specifications. So change descriptive response codes
like "400_auth" and "400_anauth" to "400_0" and "400_1" for all
such endpoints. Also make the necessary changes in openapi.py so
as to be able to read the schema in such cases and generate example
in such cases.
