20-VI-06: cgn 007

• Added print-graphic, to print directly from cgn.
• Modified plot-function. Now can be used to plot g(x,y), not only f(x).
• Added save-cgn, to save.
• Added load-cgn, to load.
• Added with-gnuplot, a macro which should be the prefered way to use cgn.
• Added the *os* special variable, to use with with-gnuplot to let cgn know which os is running. This is used to print, at the moment.
• Updated cldoc documentation.