DataKind shouldn't be present in our public API.

[Ivanidzo4ka]

We need to replace places like this

machinelearning/src/Microsoft.ML.Data/Transforms/TypeConverting.cs

Line 542 in 13b3339

public readonly DataKind OutputKind;

machinelearning/src/Microsoft.ML.Data/DataLoadSave/Text/TextLoader.cs

Line 45 in 832ecad

public Column(string name, DataKind? type, int index)

to proper .net type support.