title: get error as string from error interface
body: <p>How to get error as string from an error interface?</p>
  
  <p>I want to assign <code>ERROR: Fake error!</code> to a variable and then convert it to a slice <code>[]byte(error_str)</code></p>
  
  <pre><code>prefix_err := "ERROR: "
  
  defer func() {
      if err := recover(); err != nil {
          // get error message from "err" as string
      }
  }()
  
  panic("Fake error!")
  </code></pre>