fixed the enclosing problem happened when the building itself is already enclosed,

fixed the enclosing problem happened when the building itself is already
enclosed;
in create_side_surface_for_each_floor(), made it possible for the loop
to reach to segment between the starting point and the end point;
applied horizontally continuous uv coordniate to floor board to apply
non-plain floor texture;
removed .filters file;
changed texture file names to meaningful names.