This is a preparatory commit for using isort for sorting all of our
imports, merging changes to files where we can easily review the
changes as something we're happy with.
These are also files with relatively little active development, which
means we don't expect much merge conflict risk from these changes.
This adds a couple new tools that can be used to determine whether a
particular change in Zulip's backend markdown processor would impact
the rendering of historical messages, without a human actually looking
at the message content. This is a useful way to verify whether a
change to our markdown syntax is likely to create problems.
[commit message and code tweaked by tabbott]
Tim Abbott
rht
Anders Kaseorg
paxapy