Setup Visual Studio to use WinMerge

I've made this change on a number of occasions, so I'm linking this here to hopefully save myself and / or someone else some time in setting this up.

Credit to Paul Bouwer for his blog post Replace diff/merge tool in Visual Studio Team System with WinMerge ( ).

Paul Bouwer's blog post

And for, in my opinion, a better formula than the one described in the article, check out Kashiraja's comment.

Kashiraja's comment