title: Use of unicode characters in Haddock documentation
body: <p>Haddock seems to incorrectly re-encode non-ASCII characters in the documentation in UTF-8 encoded source files. I often need to include mathematical formulas in the documentation and they are much more readable if some common math symbols such as summation (∑) can be used. </p>
  
  <p>However, after running the files through haddock, these symbols become blank squares. 
  Haddock has the option <code>--use-unicode</code> but that just converts function arrows in function signatures etc. into unicode characters, while still breaking the actually documentation.</p>
  
  <p>Even better would be if this can be controlled from <code>cabal haddock</code>!</p>
  
  <p>I'm using Haddock version 2.9.4.</p>