[pstricks] pstricks-add documentation

[cpiateck at univ-orleans.fr]

When trying to plot with the algebraic option I find that the
documentation is not enough precise on the algebraic use of functions as
Sum, Ceiling...

Is there a place where we can find some more developped documentation.

Secondly, could the command ArrowInside be used with all type of curve, even
those plotted with the differential equation command.

Third, pstricks-add as a parametric plot command. Why not an implicit one.
Of course, pst-func as such a function but we cannot use the algebraic
parameters.

    Thanks

    cyrille