added lost Strikeout file

java/markup/Strikeout.java

@@ -0,0 +1,24 @@
+package markup;
+
+import java.util.List;
+
+public class Strikeout extends AbstractMarkup {
+    public Strikeout(List<MarkupElement> elements) {
+        super(elements);
+    }
+
+    @Override
+    public void toMarkdown(StringBuilder sb) {
+        toMarkdown(sb, "~");
+    }
+
+    @Override
+    public void toHtml(StringBuilder sb) {
+        toHtml(sb, "s");
+    }
+
+    @Override
+    public void toTex(StringBuilder sb) {
+        toTex(sb, "\\textst");
+    }
+}