title: CodeMirror delete a editor instance
body: <p>I am using CodeMirror to do some syntax highlighting in my web. I've created two radio buttons in my html. And my JavaScript code is as follows:</p>
  
  <pre><code>if(flag == "C")
      Editor = CodeMirror.fromTextArea(textArea, {
      lineNumbers: true,
      matchBrackets: true,
      mode: "text/x-csrc"
  });
  else if(flag == "Cpp")
      Editor.off(0);
      Editor = CodeMirror.fromTextArea(textArea, {
      lineNumbers: true,
      matchBrackets: true,
      mode: "text/x-c++src"
  });
  </code></pre>
  
  <p>It does complete the function of syntax highlighting, but the problem is when I click the radio button multiple times, it just create as many as I click, and this is annoying. So I am wondering is there any way to delete the previous editor instance before I create a new one?</p>