In order to use this you have to:
aptitude install lua5.2 lua-posix
or equivalent.

So:
requirements are lua-posix and lua5.2 or higher for now


TODO:
Package it as a normal package

How this works:
Your firewall description is nothing more than a set of :rules() for a set of
objects. :rules() are essentially a set of functions that transform into a set
of nested arrays and command line strings.
These nested arrays are nothing more than a complex way of writing an iptables
command line. These nested tables are parsed by fw/expand.lua .
Something like this:
{"/bin/echo","hello","dave"} will turn into exactly: /bin/echo hello dave.
But:
{"/bin/echo","hello",{"dave","john"}} will turn into:
/bin/echo hello dave
/bin/echo hello john
{"/bin/echo","hello","dave","john"} will turn into:
/bin/echo hello dave john
BUT:
{"/bin/echo","hello",{f=1,"dave","john"}} will also turn into:
/bin/echo hello dave john
a key f in an array means flatten. It will not explode the array.

Now let's see what a :rules() does:
net:rules()
	self:allow{proto.ssh}
}
turns into
iptables --append "name ofthisnet" --destination-port 22 --jump ACCEPT
net:rules()
	self:allow{proto.ssh,{ net1, net2 }}
}
iptables --append "name ofthisnet" --destination-port 22 --in-interface net1  --jump ACCEPT
iptables --append "name ofthisnet" --destination-port 22 --in-interface net2  --jump ACCEPT

etc...

But it is what it is: a big shellscript generator, and as such we can also say:
"nah" instead of proto or whatever. And it will output nah, and iptables will complain when you run it.