static <T> Writer<T> attr(
		final String name,
		final Object value
	) {
		return attr(name).map(data -> value);
	}
Writes the attribute with the given {@code name} and a constant
{@code value} to the current <em>outer</em> element.

{@snippet lang="java":
final Writer<MyObject> writer = elem("element", attr("version", "1.0"));
}

@param name the attribute name
@param value the attribute value
@param <T> the writer base type
@return a new writer instance
@throws NullPointerException if one of the {@code name} is {@code null}
jenetics.xml/src/main/java/io/jenetics/xml/stream/Writer.java