Merge pull request #4 from terrajobst/master

Tests
Reimplemented GenerateNuSpec and ReadPackagesConfig tasks to use NuGet classes instead of XDocument.
Added support for 'allowedVersions' configuration.
Merged VersionSpec into Version metadata.
Made naming consistent with NuGet.Core.
Fixed typos.
Merge pull request #19 from kovalikp/issue17

Issue17