Need to support more types than string and float

[maryamariyan]

From @eerhardt on Apr 12, 2018, 6:52 AM PDT

See code in machinelearning/src/Microsoft.MachineLearning.EntryPoints/TextLoader.cs

	private string TypeToName(Type type) 
	{ 
	if (type == typeof(string)) 
	return "TX"; 
	else if (type == typeof(float) || type == typeof(double)) 
	return "R4"; 
	else 
	throw new Exception("Type not implemented or supported."); //Add more types. 
	} 

(Refers to Lines 70 to 78 in 6e74d72)

We should fill all supported types out and add tests.