title: 'tostring' function in pine-script
body: <p>I'm trying to create plot name based on input value. However getting error (in line#6).
  Below is my code.
  Thank you so much for your time and reply.</p>
  <pre><code>//@version=4
  study(title=&quot;EMA&quot;, shorttitle=&quot;ema&quot;, overlay=true)
  ema_len = input(50, title='Period')
  EMA = ema(close, ema_len)
  plot_name = 'EMA' + tostring(ema_len)
  plot(EMA, title=plot_name)
  </code></pre>
  <p><strong>Error message:</strong></p>
  <p><code>Add to Chart operation failed, reason: line 6: Cannot call 'plot' with 'title'=string. The argument should be of type: const string</code></p>