[dune-fem] LocalFunctionAdapter

[Agnese, Marco]

Hi Andreas,
to recap the class LocalAnalyticalFunction which I implemented simply store a reference to a C++ function

RangeType f(const DomainType& x,const double& t,const EntityType& entity)
{
 //do stuff
}

and add all the necessary types/methods in such a way you can pass it to the LocalFunctionAdpater to obtain a GridFunction.

I would like to add a class AnalyticalFunctionAdapter do Dune-Fem that takes a C++ function and return a GridFunction (using the aforementioned LocalAnalyticalFunction and LocalFunctionAdapter).

In this way would be very handy for everybody to transform the c++ fucntion f into a GridFunction.

Cheers,
Marco.