[WIP] F# Generative Type Provider vNext (such as it should be)

Project reference for generative type provider, that should

• Run on net45 with FSharp.Core.dll v4.0.
• Run on Xamarin (Support PCL Profile259)
• Support Fable
• Allow consumer to use FSharp.Core.dll v4.1 in target runtime (quotation rewrite or binding redirects)
• Run on netcore2.0 and/or NetStandard2.0 (one day ... maybe... visualfsharp#2406)