* The library must provide an interface for setting each of the options
  controlled by the documented Nmap command-line options.

* The library must allow setting scan options through a command-line-like
  string.

* The library must be portable to all systems that nmap currently supports.

* It must be possible to run a scan in a nonblocking fashion and receive
  periodic status updates.

* It must be possible to run more than one scan at a time, and to get the
  results of a finished scan as soon as it is finished, even if it was started
  after another scan that has not finished.