Upgrade nuget deps, rm packages, .gitattributes

This is a cleanup PR of the project repo. It includes:

* Add the default .gitattributes file from GitHub for Windows - this is necessary and addresses line ending normalization
* Add the packages folder to the .gitignore file - these should not be part of the repo to reduce unnecessary repo bloat
* Remove the packages folder from the repo
* Upgrade NuGet packages to latest versions

This cleanup represents best practices for .NET git repos and if you have any questions let me know. If for some reason the maintainers would wish to have these as separate PRs, I can do that as well.