Improve jsdoc for API return values (#3327)

* Add jsdoc for usePromises, add @link for callbacks

* Update petstore samples

* Improve jsdoc for void return type + usePromises

* Add back curly brackets correctly in model template

* Add link to Promise doc in jsdoc comment

* Fix jsdoc annotation for callApi method

The return type annotation was also broken here.

samples/client/petstore/javascript-promise/src/ApiClient.js

@@ -154,7 +154,7 @@
   /**
    * Checks whether the given parameter value represents file-like content.
    * @param param The parameter to check.
-   * @returns {Boolean} <code>true</code> if <code>param</code> represents a file. 
+   * @returns {Boolean} <code>true</code> if <code>param</code> represents a file.
    */
   exports.prototype.isFileParam = function(param) {
     // fs.ReadStream in Node.js (but not in runtime like browserify)
@@ -206,7 +206,7 @@
 
   /**
    * Enumeration of collection format separator strategies.
-   * @enum {String} 
+   * @enum {String}
    * @readonly
    */
   exports.CollectionFormatEnum = {
@@ -342,7 +342,8 @@
    * @param {Array.<String>} contentTypes An array of request MIME types.
    * @param {Array.<String>} accepts An array of acceptable response MIME types.
    * @param {(String|Array|ObjectFunction)} returnType The required type to return; can be a string for simple types or the
-   * constructor for a complex type.   * @returns {Promise} A Promise object.
+   * constructor for a complex type.
+   * @returns {Promise} A {@link https://www.promisejs.org/|Promise} object.
    */
   exports.prototype.callApi = function callApi(path, httpMethod, pathParams,
       queryParams, headerParams, formParams, bodyParam, authNames, contentTypes, accepts,