Mostly, this is a change in ordering to make more sense, but we also
fix several names that were clearly confusing.
We restore the convention that each endpoint has the same title at the
top of the page as what we have in the sidebar menu, which appears to
have been violated in many recent updates to API documentation.
api docs filenames are basically the operationId of their endpoint
in zulip.yaml with `_` replaced by `-`. But some operationIds have
changed, so change the affected filenames. Make changes in other
files accordingly.