- Update actions/checkout to v2.
- setup-dotnet requires specific version or a wildcard so I changed it to 5.0.x so it targets any 5.0 version.
- Updated Raylib-cs.Tests to target net5.0 as we can now use it properly.
- Set libraries to target netstandard2.1 and updated tests to net5.0. Still learning about the new features. Libraries may also change to net5.0
later if the newer features are useful enough to include directly in the library.
- Removing Platform.cs which was only used by netfx.