Make instantiation of cost function internal

[romangrothausmann]

Why is the (special) cost function (SingleImageCostFunction) not instantiated internally? From the publication it seems that

PathFilterType :: CostFunctionType :: Pointer cost =  
   PathFilterType :: CostFunctionType :: New ();

PathFilterType :: Pointer pathFilter = PathFilterType :: New ();
pathFilter -> SetCostFunction ( cost );

is expected when employing SpeedFunctionToPathFilter.
What cases could there be where the cost function here would not be the predefined SingleImageCostFunction?
If there are no other, the instantiation of cost function could be done internally, so that it is not necessary when using SpeedFunctionToPathFilter.

[thewtex]

@romangrothausmann it sounds reasonable to instantiate a reasonable default 👍 .