Fix release script for windows build

Fix release script for windows build, which had previously issues to deploy the nuget package

.NET Framework 4.8 version

Publish a Net Framework 4.8 version in addition to the Core build. Use windows nodes for travis to achieve this.

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;

Add possibility to do cycle checks

This PR introduced new rules for cycle checks within slices through your architecture.
See: #15

Improvements to Fluent Syntax

ImplementInterface, AreCalledBy, etc. are now available.

Better extension method support

Fixed an issue with missing extension methods

Added support for extension methods

Added support for extension methods