title: Convert DateTime.Now to a valid Windows filename
body: <p>I have had this issue quite a few times and have just been using a workaround but thought I would ask here in case there is an easier option. When I have a string from <code>DateTime.Now</code> and I then want to use this in a filename I can't because Windows doesn't allow the characters / and : in filenames, I have to go and replace them like this:</p>
  
  <pre><code>string filename = DateTime.Now.ToString().Replace('/', '_').Replace(':', '_');
  </code></pre>
  
  <p>Which seems a bit of a hassle, is there an easier way to do this? Any suggestions much appreciated.</p>