title: AttributeError: module 'PySimpleGUI' has no attribute 'theme'
body: <p>I have try</p>
  <pre><code>sg.theme('DarkAmber')
  </code></pre>
  <p>but I got the error</p>
  <blockquote>
  <p>&quot;AttributeError: module 'PySimpleGUI' has no attribute 'theme'&quot;</p>
  </blockquote>
  <pre><code>software version:
  python3.6, PySimpleGUI version:4.16.0
  platform: ubuntu 16.04
  </code></pre>