Update _metadata

Added NuGet 2.6 to make it come on the top on  docs.nuget.org
Update NuGet-2.6.markdown

Added NuGet split information
Update NuGet-2.6.markdown

updated the text
Update NuGet-2.6.markdown

Updated the links for vsix.
Merge pull request #113 from deepakverma/nuget-next

Nuget next