Incremented major version, to indicate:

- The Spec attribute is the new name of the AutoDataTheory attribute.

- The AutoMoq feature is integrated, so the AutoFixture.AutoMoq nuget
  package does not need to be installed. Just add the Moq reference to
  create a mock instance.

- The Xunit features, such as Fozen and Greedy iherited from
  CustomizeAttribute, are still supported.