NAT-PMP is the direct concurrent to the UPnP IGD specification. It is providing
a way to do NAT traversal.  libnatpmp is an attempt to make a portable and
fully compliant implementation of the protocol for the client side. It is
based on non blocking sockets and all calls of the API are asynchronous. It
is therefore very easy to integrate the NAT-PMP code to any event driven code.
