improve image search

use object instead of a string for the imagefilters

README.md

@@ -35,7 +35,13 @@ Adding filter(s) for the Image Search
 ```js
 Bing.images("Ninja Turtles", function(error, res, body){
   console.log(body);
-}, {imagefilters: 'Size:Small+Color:Monochrome'});
+  }, 
+  {
+    imagefilters: {
+      size: 'small',
+      color: 'monochrome' 
+    }
+  });
 ```
 Accepted filter values:
 * Size:\<Small | Medium | Large\>

lib/bing.js

@@ -139,13 +139,29 @@ Bing.prototype.search = Bing.prototype.web;
  *
  * @param {Object} options            Options to command, allows overriding of
  *                                    rootUri, accKey (Bing API key),
- *                                    userAgent, reqTimeout, top, skip
+ *                                    userAgent, reqTimeout, top, skip,
+ *                                    imagefilters
  * @function
  */
 Bing.prototype.images = function(query, callback, options) {
+    if (options.imagefilters) {
+      var filterQuery = '';
+      var filters = Object.keys(options.imagefilters);
+      filters.map(function(key, i) {
+        filterQuery += capitalizeFirstLetter(key) + ':';
+        filterQuery += capitalizeFirstLetter(options.imagefilters[key]);
+        if (i < filters.length - 1)
+          filterQuery += '+';
+      });
+      options.imagefilters = filterQuery;
+    }
     this.searchVertical(query, "Image", callback, options);
 };
 
+function capitalizeFirstLetter(s) {
+  return s.charAt(0).toUpperCase() + s.slice(1);
+}
+
 
 module.exports = Bing;