anchor.diff:                  | "monoandroid50" -> Some (MonoAndroid MonoAndroidVersion.V5)
                   | "monoandroid60" -> Some (MonoAndroid MonoAndroidVersion.V6)
                   | "monoandroid70" | "monoandroid7.0"-> Some (MonoAndroid MonoAndroidVersion.V7)
  +                | "monoandroid71" | "monoandroid7.1"-> Some (MonoAndroid MonoAndroidVersion.V71)
                   | "monomac" | "monomac10" | "monomac1" -> Some MonoMac
                   | "xamarinios" | "xamarinios10" | "xamarinios1" | "xamarin.ios10" -> Some XamariniOS
                   | "xamarinmac" | "xamarinmac20" | "xamarin.mac20" -> Some XamarinMac
  
positive.code:     | V5
      | V6
      | V7
      member this.ShortString() =
          match this with
          | MonoAndroidVersion.V1    -> ""
  
negative.code:         | MonoAndroid MonoAndroidVersion.V5 -> [ MonoAndroid MonoAndroidVersion.V44 ]
          | MonoAndroid MonoAndroidVersion.V6 -> [ MonoAndroid MonoAndroidVersion.V5 ]
          | MonoAndroid MonoAndroidVersion.V7-> [ MonoAndroid MonoAndroidVersion.V6; DotNetStandard DotNetStandardVersion.V1_6 ]
          | MonoAndroid MonoAndroidVersion.V71-> [ MonoAndroid MonoAndroidVersion.V7 ]
          | MonoTouch -> [ DotNetStandard DotNetStandardVersion.V1_6 ]
          | MonoMac -> [ DotNetStandard DotNetStandardVersion.V1_6 ]
          | Native(_) -> [ ]
  