title: How to span columns in NSGridView or NSTableView
body: <p>I've looked everywhere and haven't found much built-in functionality for spanning columns or rows of either the NSGridView or the NSTableView. At this point I'm thinking I'm going to have to either override some methods or look for another control. I haven't been working in OSX for very long, and to make it worse I'm in Xamarin which doesn't have much out there at quite yet. If you have an answer in cocoa I could translate (or at least try).</p>
  
  <p>Is there something else out there that would fit my needs better? I need a view based grid of some sort that can span rows/columns. Could someone at least point me in the general direction of a solution? Thanks!</p>