Idea: Increment approach for ADX about stock.indicators

[DaveSkender]

Thanks @ingted. I'll keep this in mind when getting back to:

• #1018

It might make sense for our next v3 preview to focus on providing all the static increments functions as part of the public API. That would allow users to do their own instrumentations. Adding something like this makes sense.

We've already started down this path anyway:

Stock.Indicators/src/e-k/Ema/Ema.Observer.cs

Lines 43 to 45 in fc34f3d

	// incremental calculation
	internal static double Increment(double newValue, double lastEma, double k)
	=> lastEma + (k * (newValue - lastEma));

Stock.Indicators/src/s-z/Sma/Sma.Observer.cs

Lines 40 to 58 in fc34f3d

	// incremental calculation
	internal static double Increment(
	List<(DateTime Date, double Value)> values,
	int index,
	int lookbackPeriods)
	{
	if (index < lookbackPeriods - 1)
	{
	return double.NaN;
	}
	double sum = 0;
	for (int i = index - lookbackPeriods + 1; i <= index; i++)
	{
	sum += values[i].Value;
	}
	return sum / lookbackPeriods;
	}

[DaveSkender]

Related to #1091