(so that stale test files, which can be very large, get wiped out)

Patch by Ben Hayden.

concurrent.futures.

concurrent.futures.

whole HTTP exchange, not only the opening.

for the names of optional and positional arguments in help messages.

The options listed in the table are now links to their documentation,
and the table uses compact markup to make it easier to read and edit.
First proposed in #10998.