title: Restrict kivy's TextInput to only ascii characters
body: <p>Please is there a way i can make a TextInput to disallow non ascii characters. So that when text is entered into the TextInput if a non-ascii character is typed it will not be added to TextInput. Just like the way one uses int filter, thus only whole numbers will be allowed in the TextInput<br>
  Please an example code would very be helpful. Thanks in advance</p>