Tracebox, a middlebox detection tool

Basic use of the Lua API

When run, the scripts have preset global variables and functoin, listed in Globals. The most basic script is made of 3 parts:

Probe packet definition, using successive concatenation of packet layers, see Globals.
```
pkt = ip{dst='185.31.18.133'} / tcp{dst=80}
```
Callback function definition, which will be called after each probe packet has been echoed back by intermediate routers on the path, see Globals:tracebox_callback.
```
function cb(ttl, r_ip, probe, rcv, mod)
    print('At hop ' .. ttl)
    print('Received: ' .. tostring(rcv))
end
```
tracebox() function call, see Globals:tracebox, with the created probe packet and callback function, which will run tracebox and call the callback with the detected packet modifications and return the final received packet received from the target, if any.
```
result = tracebox(pkt, {callback='cb'})
print(tostring(result))
```

Global functions and objects provided by TraceBox

__cpp_obj	Abstract type for all custom classes exposed from cpp, exposed to lua with reference couting.
Base_Object	Abstract type, providing the basic methods supported by most objects, inherits from __cpp_obj.
DNS	The DNS Layer
FWFilter	A simple firewall rule on the host machine.
ICMP	The ICMP Layer, inherits from Base_Object
IP	The IP Layer, inherits from Base_Object
IPOption	Options for the IP Layer, inherits from Base_Object
IPv6	The IPv6 Layer, inherits from Base_Object
IPv6SegmentRoutingHeader	The IPv6SegmentRoutingHeader Layer, inherits from Base_Object
Packet	An object representing a Packet, inherits from Base_Object
PacketModifications	A set of modifications between packets
PartialTCP	The PartialTCP Layer, inherits from Base_Object This denotes a embedded TCP layer in an ICMP payload that has been cut.
Raw	The Raw Layer, inherits from Base_Object
TbxSniffer	An object that will intercept packets
TCP	The TCP Layer, inherits from Base_Object
TCPEDO	The TCP Edo option
TCPOption	Options for the TCP Layer, inherits from Base_Object
TCPTFO	The TCP Fast Open option
TCPTimestamp	The TCP Timestamp option
UDP	The UDP Layer, inherits from Base_Object