Supporting shared projects

[cphillips83]

🚀 Feature Requests

Please add *.projitems to the search pattern in https://github.com/NuKeeperDotNet/NuKeeper/blob/master/NuKeeper.Inspection/RepositoryInspection/ProjectFileReader.cs#L41

Describe the feature

Shared projects utilize 2 files a *.shproj which include all the pieces needed for msbuild to automagically include the source in the target project and a *.projitems file which is basically like a (cs/fs/vb)proj file, these can include references to auto merge in to the target project.

[cphillips83]

As a working around, you can rename the *.projitems file to a *.csproj file and then update the reference in the *.shproj file as well as any places you included a reference to the shared project. This will let nukeeper inspect work but it will fail to update with an error but this at least lets you check versions.