(the butter, the money of the butter, and the *bip* of the Dairywoman).

 - Add a -dyn option that parses (with the last command) the end of the rif file
 - Add a -pdf option
 - Add the possibility to call the GnuplotRif main function from a ocaml program

Actually, I've simplified the code a lot while being more efficient.

1) Instead of generating explicitely a gnuplot data file (to remove
#outs/#step, etc), I use a sed/grep script file (cf util/read-rif.sh)
2) Instead of calibrating the display while generating this file in ocaml, I do
it directly via gnuplot
3) the dynamic part relies on the Unix last command