title: Smart-table date and amount sorting which is in string format
body: <p>In smart-table, sorting is easy. But when the date and amount are in string format, how to sort? </p>
  
  <pre><code>app.controller('basicsCtrl', ['$scope', function (scope) {scope.rowCollection = [
  {firstName: 'Laurent', lastName: 'Renard', birthDate:'1987-05-21', balance: '1,20,000', email: 'whatever@gmail.com'},
  {firstName: 'Blandine', lastName: 'Faivre', birthDate: '1987-04-25', balance: '2,000', email: 'oufblandou@gmail.com'},
  {firstName: 'Francoise', lastName: 'Frere', birthDate: '1955-08-27', balance: '4,23,000', email: 'raymondef@gmail.com'}];
  }]);
  </code></pre>
  
  <p>I am not able to use, the format function inside my json. Its throwing error.</p>
  
  <pre><code>formatFunction: function (value, formatParameter) {
  return value[0];// some function to change string to date.
  }
  </code></pre>
  
  <p>Following this doc. <a href="http://lorenzofox3.github.io/smart-table-website/" rel="nofollow">http://lorenzofox3.github.io/smart-table-website/</a></p>
  
  <p>Is there anyone to help me? I am new to this area...</p>