Collapsed plot and nplot into a single method, so it can further specialised, plot now can
take lists or a single narray for y & x. Now uses a binary format for communicating with
gnuplot, should be faster for big plots. The keywords are now as nplot and therefore
slightly incompatible with earlier plot calls, namely :label becomes :legends and must
take a list, ditto :styles. Made the temporary plot file directory more
platform independent, with preliminary support for Windows and clisp, thanks to Mirko
Vukovic for prototyping. Updated mudballs definition file to be functional until the
distribution is verified.