added any as valid value for the trusted_proxy adjustable

[Estartu]

Backgound is when waitress is running inside a container, any
request is originates from the gateway of the container network, not
from the outside ip. The container network changes every time the
container is restarted to a random new network number. So setting one
IP as trusted_proxy isn't possible but still needed as most of the time
an reverse proxy is between the client an the container. So if it's
ensured that only requests from the reverse proxy can reach the
container, trusting any host is not a problem.

[digitalresistor]

I would prefer not to use something that could potentially be a valid remote_peer. I would accept this if it was changed to use * instead.

[Estartu]

remote_peer is a IP address and any is neither a valid ipv4 nor ipv6 address. I don't see a potential mixup. But i have no problem in changing it. I will update the pull request shortly.

[digitalresistor]

remote_peer may also be set to localhost for instance in the unix socket case. There was also a case whereby remote_peer may go through a reverse DNS lookup which could potentially return a hostname, but I may be mistaking that with the address we listen to.

Either way, thank you for changing it.