Added JSDoc for Neo4jError class

So that it becomes visible in the API docs at
http://neo4j.com/docs/api/javascript-driver/current/.

Author: lutovich

src/v1/error.js

@@ -39,8 +39,17 @@ function newError(message, code="N/A") {
   return new Neo4jError(message, code);
 }
 
+/**
+ * Class for all errors thrown/returned by the driver.
+ */
 class Neo4jError extends Error {
-  constructor( message, code="N/A" ) {
+
+  /**
+   * @constructor
+   * @param {string} message - The error message.
+   * @param {string} code - Optional error code. Will be populated when error originates in the database.
+   */
+  constructor(message, code = 'N/A') {
     super( message );
     this.message = message;
     this.code = code;