title: Using mix of AND and OR clause in sails and waterline
body: <p>How can I use OR and AND clause in Sailsjs and its ORM Waterline? For example I have a table of books</p>
  
  <pre><code> _______________________________________
  | book_name | author   | free  | public |  
   _______________________________________
  | Book-A    | Author-1 | false | true   |
   ---------------------------------------
  | Book-B    | Author-1 | true  | true   |
   ---------------------------------------
  | Book-C    | Author-1 | false | false  |
   ---------------------------------------
  | Book-D    | Author-2 | true  | true   |
   ---------------------------------------
  </code></pre>
  
  <p>I want to get Books by Author-1 which are either public or free,  which is Book-A and Book-B. How do I write this query with Sails.js       </p>