In our inbox-writing code paths, ->getline as an OO method may
be confused with the various definitions of `getline' used by
the PSGI interface. It's also easier to do: "perldoc -f readline"
than to figure out which class "->getline" belongs to (IO::Handle)
and lookup documentation for that.
->print is less confusing than the "readline" vs "getline"
mismatch, but we can still make it clear we're using a real
file handle and not a mock interface.
Finally, functions are a bit faster than their OO counterparts.