title: ** is new power operator instead of power() in php
body: <p>How to use new version of Power operator instead of <code>pow()</code> in new version of php (5.6)?
  Like:</p>
  <pre><code>echo pow(2,3);
  </code></pre>
  <p>Why output of this line is 512 not 64?</p>
  <pre><code>2 ** 3 ** 2;
  </code></pre>