Between 2.0.x and 2.1.x

* Better ming Windows build support.
* Added -E flag to allow multicast ethernet traffic.

* Added -L flag to allow set TTL for registration packet.
This is an advanced flag to make sure that the registration packet is dropped immediately when it goes out of local nat
so that it will not trigger some firewall behavior on target peer. Actually, the registration packet is only expected to
make local nat UDP hole and is not expected to reach the target peer, see https://tools.ietf.org/html/rfc5389.
To achieve this, the flag should be set as nat level + 1. For example, if we have 2 layer nat in local, we should set
-L 3.
Usually we know exactly how much nat layers in local.
If we are not sure how much nat layers in local, we can use traceroute on Linux to check. Following example shows a local
single layer nat because on second jump it shows a public ip address. In this case it should set -L 2.
$ /usr/sbin/traceroute -w1 8.8.8.8
traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets
 1  192.168.3.1 (192.168.3.1)  0.464 ms  0.587 ms  0.719 ms
 2  112.65.17.217 (112.65.17.217)  5.269 ms  7.031 ms  8.666 ms

But this method is not always work due to various local network device policy.