Switch examples to .NET 8

SFML is primarily focussing on .NET Standard 2.0 and/or "mondern" .NET
as such it makes sense to have all examples on .NET 8 and one example
demonstrating .NET Framework support

Bump version to 2.6.1

Bump package versions to 2.6.0

Remove unnecessary dependencies for the Audio module

Generate NuGet packages on build

Fixed addition/subtraction for Vector3f

Merge pull request #111 from SFML/feature/2.3_prep

Bumped version number to 2.3 and updated readme.txt

Merge pull request #103 from zsbzsb/update/version_number

Updated version number to 2.2

Updated version number

Updated the website links in readme.txt