Nuspec Support

This patch adds an `Analyzer` which will parse [Nuget](http://nuget.org) [Nuspec](docs.nuget.org/docs/reference/nuspec-reference‎) files. This is not complete support for .NET, but it is a very basic start.

A Nuspec file is not terribly different from a Maven POM. It defines the Author and possibly Owners, ID, and Version.

The `ArchiveAnalyzer` has been modified as well to handle `nupkg` files, which are just ZIP files containing a `nuspec` and the assembly or other dependencies.