Add support for nuget pack -Verbosity switch

As of NuGet 2.0, nuget pack -Verbose has been replaced with nuget pack -Verbosity.
Version property still kept for backward compatibility.
Add support for nuget pack -Properties switch

One of the most handy things this does is allow you to specify the build configuration:
  nuget pack foo.nuspec -Properties Configuration=Release
Merge pull request #41 from twistedstream/master

Add support for nuget pack -Verbosity and -Properties switches