- added param 'material_file_extension' to the Options class, it specifies the material file suffix, default is ".mat" as it was before, we needed it becuase Blender expects ".mtl"
- removed default and copy constructor and destructor as well as assignment operator, because these are not necessary here, see https://en.cppreference.com/w/cpp/language/rule_of_three
(Thanks to Philipp Auersperg-Castell for the patch )
7e670896a6