add method that returns a string representation of the tags in Tags

pdb-api/src/main/java/org/lucares/pdb/api/Tags.java

@@ -225,4 +225,22 @@ public class Tags {
 		return new Tags(filename);
 	}
 
+	public String asString() {
+
+		final StringBuilder result = new StringBuilder();
+		final SortedSet<Tag> tags = toTags();
+
+		for (final Tag tag : tags) {
+			if (result.length() > 0) {
+				result.append(", ");
+			}
+
+			result.append(tag.getKey());
+			result.append(":");
+			result.append(tag.getValue());
+		}
+
+		return result.toString();
+	}
+
 }