[header] Support header comments so line breaks properly with pretty …

…print

License headers will be comments at start of html.  Pretty print today does not line break
when it writes it thus it is not properly pretty printed.  This patch looks for usage of
pretty print and fact that 'accum' is empty to ensure the proper line break.

src/main/java/org/jsoup/nodes/Comment.java

@@ -37,12 +37,23 @@ public Comment setData(String data) {
     }
 
 	void outerHtmlHead(Appendable accum, int depth, Document.OutputSettings out) throws IOException {
-        if (out.prettyPrint() && ((siblingIndex() == 0 && parentNode instanceof Element && ((Element) parentNode).tag().formatAsBlock()) || (out.outline() )))
+        if (out.prettyPrint() && ((siblingIndex() == 0 && parentNode instanceof Element && ((Element) parentNode).tag().formatAsBlock()) || (out.outline() ))) {
             indent(accum, depth, out);
-        accum
+        }
+
+        // Handle Header License Comment Properly under Pretty Print
+        if (out.prettyPrint() && accum.toString().isEmpty()) {
+            accum
+                .append("<!--")
+                .append(getData())
+                .append("-->")
+                .append("\n");
+        } else {
+            accum
                 .append("<!--")
                 .append(getData())
                 .append("-->");
+        }
     }
 
 	void outerHtmlTail(Appendable accum, int depth, Document.OutputSettings out) {}

src/test/java/org/jsoup/nodes/CommentTest.java

@@ -21,7 +21,8 @@ public void getData() {
 
     @Test
     public void testToString() {
-        assertEquals("<!-- This is one heck of a comment! -->", comment.toString());
+        // Tests under toString are pretty printed with first being simulated license header (no content), respect new line
+        assertEquals("<!-- This is one heck of a comment! -->\n", comment.toString());
 
         Document doc = Jsoup.parse("<div><!-- comment--></div>");
         assertEquals("<div>\n <!-- comment-->\n</div>", doc.body().html());