print out captive portal URI & pass it to bind_hook

get new MAC address during InterfaceUp event
also generate new xid on MAC change

If it's not set the kernel chooses it automatically using the IP address
of the gateway. If there are multiple interfaces (e.g. ethernet and
wireless) with the same subnet (e.g. a simple home router setup) then
this results in two default routes over the same interface. Manually
setting the interface fixes this.

some DHCP servers don't send netmask and gateway option unless
explicitly requested ...........

more content, nice formatting

ignored this file and implemented something better fitting

requires &Interface to be passed to all functions which may call
log!() because of the Config struct member

command line as well as config file
"suppress regular output, only display warnings and errors"

warn!() is not a valid name because already taken
by a global attribute

it's not like Haskell Maybe (that would be Option)
it's more like a fancy tuple

overwriting options will work this way