SDCA's L1Regularization is badly named since rename

[rauhs]

A lot of the constants of various learners got renamed to L1Regularization. But, in SDCA this isn't actually the L1Regularization as the doc also states. It's the ratio of L1/L2.

machinelearning/src/Microsoft.ML.StandardTrainers/Standard/SdcaBinary.cs

Lines 167 to 175 in 5d9e880

	// REVIEW: make the default positive when we know how to consume a sparse model
	/// <summary>
	/// The L1 <a href='https://en.wikipedia.org/wiki/Regularization_(mathematics)'>regularization</a> hyperparameter.
	/// </summary>
	[Argument(ArgumentType.AtMostOnce, HelpText = "L1 soft threshold (L1/L2). Note that it is easier to control and sweep using the threshold parameter than the raw L1-regularizer constant. By default the l1 threshold is automatically inferred based on data set.",
	NullName = "<Auto>", Name = "L1Threshold", ShortName = "l1", SortOrder = 2)]
	[TGUI(Label = "L1 Soft Threshold", SuggestedSweeps = "<Auto>,0,0.25,0.5,0.75,1")]
	[TlcModule.SweepableDiscreteParam("L1Threshold", new object[] { "<Auto>", 0f, 0.25f, 0.5f, 0.75f, 1f })]
	public float? L1Regularization;