Upgrade projects to Visual Studio 2015 format

[nzbart]

I opened the existing project in Visual Studio 2015, which prompted me to upgrade it. These are the changes that the upgrade process made.

Now that Visual Studio 2015 is provided for free for home and some commercial use, there are hopefully few people still running the older versions of Visual Studio such as 2005.

Note that I left the target framework set to 2.0 because some people may still be targeting older frameworks.

The readme should probably be updated to reflect this change. I suspect that VS 2013 should still work, however, I don't want to say that explicitly because I haven't got VS 2013 and therefore can't test it. I'm not sure whether to say that VS 2015 or VS 2013 is required, or just say that it might work in 2013 and definitely works in 2015...