fixed more doxygen documentation errors

modules/base/src/string_ref.hh

modules/bindings/pymod/naccess.py

modules/conop/src/nonstandard.hh

modules/gfx/src/entity.hh

modules/gfx/src/scene.hh

modules/gui/pymod/__init__.py

modules/img/alg/src/dft.hh

modules/io/doc/io.dox

modules/io/pymod/__init__.py

modules/io/src/mol/star_parser.hh