Possibly merge the DLLs for less setup

[FreezyExp]

Only referencing 'NSubstitute.dll' gives compile errors.

Using ilmerge https://github.com/dotnet/ILMerge the DLLs can be combined into one

which is usually bad practice as it leads to unnecessary bloat, but for editor only things like this who cares? 😏

run: ILMerge.exe /xmldocs /out:merged\NSubstitute.dll NSubstitute.dll Castle.Core.dll System.Threading.Tasks.Extensions.dll

Now only referencing 'NSubstitute.dll' is enough to make it work.

Thanks for sharing this repository with the world 😄