Support function for lookup column construction. (#25)

README.md

@@ -118,7 +118,7 @@ Collection object shown with defaults:
   // specify an alternative parent container for the menu
   menuContainer: document.body,
 
-  // column to search against in the object
+  // column to search against in the object (accepts function or string)
   lookup: 'key',
 
   // column that contains the content to insert by default
@@ -129,6 +129,16 @@ Collection object shown with defaults:
 }
 ```
 
+The `lookup` column can also be passed a function to construct a string to query against. This is useful if your payload has multiple attributes that you would like to query against but you can't modify the payload returned from the server to include a concatenated lookup column.
+
+```js
+{
+  lookup: function (person) {
+    return person.name + person.email;
+  }
+}
+```
+
 ### Template Item
 Both the `selectTemplate` and the `menuItemTemplate` have access to the `item` object. This is a meta object containing the matched object from your values collection, wrapped in a search result.