Upgrade to xUnit 2

Fixes #628 

 - [x] migrated tests over to new infrastructure
 - [x] VS runner packages included for VS2013+
 - [x] console runner included for CI scripts
 - [x] Is Appveyor Happy?
 - [x] cleanup all the things
The reason I didn't ignore it before is I didn't want the build script to have to install it every single time. That adds unnecessary time for something that doesn't change often. Instead, when we upgrade, you just delete it and run the script once, and then commit it.

But I'm open to changing it if you feel it's better this way.