title: Code Mirror Issue with show-hint async option
body: <p>I am Using Code-Mirror plugin and i am facing below issue:</p>
  
  <p>i wrote a function to get the hints from database. i am calling this function on every key press. But when i type fast without selecting from hints some letters are missing in editor as auto-complete function needs to make a rest call and get suggestions. i gave option async true to get rid off that delay. in that case suggestions are not coming up.
  Below is the code how i initialize the auto complete. i call this line of code on every key press.</p>
  
  <p>CodeMirror.showHint(instance, CodeMirror.hint.anyword, {completeSingle : false,async : false});</p>