POINT: use DxfFile struct in dxf_point_write().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
POINT: changed the return type for dxf_point_read().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
POINT: added dxf_point_free().

Signed-off-by: bert <bert.timmerman@xs4all.nl>