$^ is the one we want: include a white-space delimited list of the prerequsites
Many changes:

* Convert argv.cc to directly return a list<string> rather that muck
  around with all the intermediate argv stuff.  We're in C++, after
  all.
* Since the parser in argv.cc is stolen from Open MPI, obey its open
  source license and include a copy of its license file in the repo
  (since this is public on GitHub -- do the Right Thing).
* Remove all traces of the --delay argument.  It didn't work well in
  practice.
* Also remove all traces of the --webdir argument.  Since wifi doesn't
  reach out to the distance that we want, it doesn't make sense to
  pursue that scheme.
* Now experiments are terminated by hitting <ENTER>.  If you just hit
  <ENTER>, we go on to the next experiment.  If you type a label first
  and then hit <ENTER> that label will be used for the next
  experiment.
* Use file streams to output the CSV file so that we can render the
  output once and then send it to cout and optionally also to the CSV
  file.