Make WITH_FILTERING option inside the core

[kalwalt]

The WITH_FILTERING option is a C++ MACRO defined in the .cpp code that add an extra linear filter operation to the trans matrix. You need to build the project with that Define option and there is no way to set up with an optional argument in the constructor r other method/properties. I will remove that define and make an optional argument in the constructor for this feature. Probably the matrixlerp function add only an unuseful overhead to the code, for this reason i don't want to force the user to select it.