Restructuring namespaces

!Please be careful, this is a breaking release!

We moved some namespaces to improve the internal architecture of ArchUnitNet. The most important change for users is that Core was removed and the implementation of the loading of the architecture moved to ArchUnitNET.Loader. Therfore you should do the following replacement in your code:

using ArchUnitNET.Core; -> using ArchUnitNET.Loader;