Stop logging 404s and the like, that wasn't on purpose

[Small yet breaking!] Don't read stdin by default

This is a very rarely-used feature (at least by me, and I'm not aware of
any other users — comment if you're one!) and makes daemonizing reserve
harder, because EOF on stdin makes it exit.

For the sake of simplicity/least surprise, don't read stdin at all
unless asked to with "-stdin".

More history in 1da9f94.

Update caching strategy

- must-revalidate and no-cache have very different semantics than they
  appear to. no-cache implies what we actually need: that the browser
  should never use a cached response without checking with the server
  first.

- Ensure that the Last-Modified time is bounded at startup, in case you
  switch directories (by stopping reserve in one place and starting it
  in another.

Bump deps

Bump deps

Clock/connection fixes

Fix importmaps

This script doesn't actually have to be a module.

Forgot to generate.

Forgot to generate.

Forgot to generate.