`ProjectParser` compatibility

[lonix1]

Moved here from cake-build/cake#1662

I'm using the "incubator" version of ParseProject. Some feedback:

1. It supports this traditional style:

   <Project Sdk="Microsoft.NET.Sdk">
   </Project>

   But not this form:

   <Project>
     <Sdk Name="Microsoft.NET.Sdk" />
   </Project>

   ...Which is common in large monorepos, because lots of reusable config is hidden away in Directory.Build.props (etc.) files. It errors with "Error: Failed to parse pre VS2017 project properties".

2. It does not support nuget's new "Central Package Management" feature. So when versions are kept in a Directory.Package.props file instead of the Foo.csproj file, then the ProjectParserResult.References has null for the versions.

3. I'm using it on a monorepo with a few dozen projects, and so far (other than the above) it works quite well. Thanks!