title: How to set default date and include_blank in date_select in Rails
body: <p>I'm using <code>date_select</code> in Rails 4 and I'd like to be able to have today's date as default but also allow for the user to leave the date field blank.</p>
  <pre><code>&lt;%= f.date_select(:birthdate, {include_blank: true, default: Date.today.to_date, start_year: Date.today.year - 100, end_year: Date.today.year - 18}) %&gt;
  </code></pre>
  <p>What is the best way to allow for blank as well as have today's date appear by default when the page opens?</p>