in pydotprint, don't merge var with the same name. shared variable in update have distinct ellipse for their input and output in the graph. Both will have the same name with a different suffix.

scan documentation + scan taken outside of sandbox [ NOTE : gradient is not fully tested, so the version of scan that is outside of sandbox does not allow to compute gradients ]

When a gradient is zero because the variable has no influence on the result, now return a variable with same shape instead of a 0 scalar, so that we can rely on the shape being unchanged

added a disabled version of Mean op. That is to make the graph of compiled fct easier to read instead of having multiple op for this fct. Need to make the gradient work before enabling by default.