add_demo — Add an entry in the demos list
add_demo(title,path)
a character string, the demo title
a character string, the path of the scilab script associated with the demo
This function adds a new entry in the demos list. The demo should be
executed by a Scilab script file. If the given title
already exists
in the demo list associated with the same file nothing is done.
The function checks if the file exist.