This change makes .gitignore viewable in snes9xw.sln. It also updates the solution to be opened in Visual Studio 2017 by default. This doesn't prevent it from being opened in VS15 for those not ready to make the switch.
add snes9x program-generated files to .gitignore
Added generated .gitignore file from https://www.gitignore.io using keywords 'C', 'C++', 'VisualStudio'
