add solutions for hw7 (markup) and tests

java/markup/Text.java

@@ -0,0 +1,24 @@
+package markup;
+
+public class Text implements MarkupElement {
+    private final String text;
+
+    public Text(String text) {
+        this.text = text;
+    }
+
+    @Override
+    public void toMarkdown(StringBuilder sb) {
+        sb.append(text);
+    }
+
+    @Override
+    public void toHtml(StringBuilder sb) {
+        sb.append(text);
+    }
+
+    @Override
+    public void toTex(StringBuilder sb) {
+        sb.append(text);
+    }
+}