title: make variant constructors public in .mli
body: <p>Consider <code>something.ml</code>:</p>
  
  <pre><code>type some_type =
    | This
    | That
  </code></pre>
  
  <p>Then, I can implement <code>main.ml</code> like this:</p>
  
  <pre><code>let x = Something.This
  </code></pre>
  
  <p>I want to create <code>something.mli</code> and keep the same functionality in <code>main.ml</code>. My first attempt was to write <code>something.mli</code> as:</p>
  
  <pre><code>type some_type
  </code></pre>
  
  <p>I thought that would make the variant constructors publicly available, but it didn't and now <code>main.ml</code> doesn't compile. Is there a way to expose the variant constructors in the <code>.mli</code>?</p>