Improve usage examples
Teach C sample code to display version information
Teach save_to_pcap to write PCap-NG files

The PCap-NG file format is used by default by Wireshark as of
Wireshark 1.8.0 (June 2012). The main advantages of PCap-NG for
capturing via Corelatus hardware are:

   - Each packet has information about which interface it came from.

   - The capture file can include information about where the capture
     came from. This allows us to add the address of the capturing
     hardware.
Add the -c switch to allow save_to_pcap to write to classic PCap