add solutions for hw7 (markup) and tests

java/markup/Paragraph.java

@@ -0,0 +1,29 @@
+package markup;
+
+import java.util.List;
+
+public class Paragraph extends AbstractMarkup implements ListItemContent {
+    public Paragraph(List<MarkupElement> elements) {
+        super(elements);
+    }
+
+    @Override
+    public void toMarkdown(StringBuilder sb) {
+        for (MarkupElement element : elements) {
+            element.toMarkdown(sb);
+        }
+    }
+
+    @Override
+    public void toHtml(StringBuilder sb) {
+        toHtml(sb, "p");
+    }
+
+    @Override
+    public void toTex(StringBuilder sb) {
+        sb.append("\\par{}");
+        for (MarkupElement element : elements) {
+            element.toTex(sb);
+        }
+    }
+}