-h, --help
Show a help message and exit.
-v, --verbose
Include all hosts and ports in the output, not only those that
have changed.
--text
Write output in human-readable text format.
--xml
Write output in machine-readable XML format. The document
structure is defined in the file
ndiff.dtd included in the distribution.
Any other arguments are taken to be the names of Nmap XML output
files. There must be exactly two.
