print more column in the profiler. Added the number of apply in the op-wise summary. Added the number of op in the single op-wise summary

small fix to the not used Mean op. Now perform() work event when axis!=None and c_code() generate code only when axis==None(only type of code implemented for now.)

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