Added support for NuGet feed discovery

Added support for NuGet feed discovery. Check https://github.com/myget/FeedDiscovery for examples. In short, users can now: DiscoverPackageSources and
Discover-PackageSources -Url "http://getglimpse.com" to add the nightlies feed to their NuGet package sources.
Merge pull request #9 from maartenba/master

Ya looks like a great idea! Happy to help out