Use tag for package version, if present

Added PackageNugetEngine as a dependency of PackageNuGet

Update for final 3.0 release

Fix broken test

Fixes nunit#1008 NUnitLite namespace not updated in the NuGet Packages

Merge pull request nunit#972 from nunit/release-3.0-RC

Release 3.0 rc

Merge pull request nunit#898 from nunit/release-3.0-beta-5

Release NUnit 3.0 Beta 5

Merge pull request nunit#788 from nunit/release-beta-4

Release beta 4

Merge pull request nunit#740 from nunit/release-beta-3

Preparing for the beta 3 release

Merge pull request nunit#651 from nunit/release-30beta2

Release 3.0 Beta 2