New shader syntax, bug fixes and improvements

🆕 New shader syntax (struct type + IComputeShader interface)
✅ Gpu.Default is now thread safe
✅ Bug fix when concurrently dispatching shaders
✅ Bug fixes when parsing some C# code to HLSL
✅ Bug fixes to constant buffer copies (thanks @john-h-k)
✅ Improved error reporting for internal failures
✅ Updated all NuGet references
🚀 Speed improvements when loading/dispatching shaders