title: libgit2sharp equivalent of "git mergetool"
body: <p>I want to use the equivalent  of "git mergetool" within libgit2sharp. Is there a sample to do this? Or do I have to dive deep and try to implement this in libgit2sharp?</p>
  
  <p>The call "git mergetool" checks if merge is required and calls the custom mergetool with a copy of the server. A proper way to call the mergetool would be usefull. I know I can read the config and search the mergetool and its "cmd" command.</p>
  
  <p>Greetings
  Thomas</p>