Public files were addressed by a 32-character account id, and a public
folder answered with JSON, so a link was unusable to send to anyone.
Accounts that signed up with a BNS name can now be addressed by it
(/p/alice.x/<drive>/<folder>/), a public folder opened in a browser is a
page with its files, small pictures and a player (tools still get JSON),
and every link and redirect on it is relative so navigate.st/s3/ serves
the same pages. Pithos shows the navigate.st/s3 address when a folder is
made public.
