title: Ocaml buffer modification specific position
body: <p>I'm currently building/concatenating pretty big strings in a program I'm developing. To give some context, the full string has the size of a terminal. This happens quite a lot since I'm developing a terminal application. I found the datastructure <code>Buffer</code>, which seems to be the most performant way to concatenate strings with the standard library.</p>
  
  <p>Is this the right choice if I also frequently need to update some part of a buffer at a specific position? Let's say character 20 to 50 ?
  Is there a better way in this case?</p>