MAJOR: tools: support environment variables in addresses

MAJOR: tools: support environment variables in addresses

Now that all addresses are parsed using str2sa_range(), it becomes easy
to add support for environment variables and use them everywhere an address
is needed. Environment variables are used as $VAR or ${VAR} as in shell.
Any number of variables may compose an address, allowing various fantasies
such as "fd@${FD_HTTP}" or "${LAN_DC1}.1:80".

These ones are usable in logs, bind, servers, peers, stats socket, source,
dispatch, and check address.