In the description of this specification, reference terms of “one embodiment”, “some embodiments”, “an example”, “a specific example”, or “some examples” are intended to indicate that specific features, structures, materials, or characteristics described with reference to the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary descriptions of the above terms do not necessarily mean a same embodiment or example. In addition, the specific features, structures, materials, or characteristics that are described may be combined in a proper manner in any one or more embodiments or examples.

Although the embodiments of the present invention have been shown and described above, it may be understood that the above embodiments are exemplary and cannot be understood as limitations to the present invention. A person of ordinary skill in the art may make changes, modifications, replacements, and variations to the above embodiments within the scope of the present invention, without departing from the principle and gist of the present invention.