Add starting point for figures in Electrical.Digital.

[maltelenz]

These originate from figures created for Wolfram System Modeler, and are likely to need cleanup and improvement.

Our one existing figure in MSL is probably a good style to follow:

ModelicaStandardLibrary/Modelica/Blocks/package.mo

Lines 159 to 180 in 3f72865

	figures = {
	Figure(
	title = "Anti-windup compensation",
	identifier = "anti-windup",
	preferred = true,
	plots = {
	Plot(
	title = "Reference tracking",
	identifier = "tracking",
	curves = {
	Curve(y = integrator.y, legend = "Reference speed"),
	Curve(y = inertia1.w, legend = "Actual speed")}),
	Plot(
	title = "Anti-windup limiter",
	identifier = "limiter",
	curves = {
	Curve(y = PI.limiter.u, legend = "Input to the anti-windup limiter"),
	Curve(y = PI.y, legend = "Controller output")})},
	caption = "%(plot:tracking) Reference speed (%(variable:integrator.y)) and the actual speed (%(variable:inertia1.w)). The system initializes in steady state, since no transients are present. The inertia follows the reference speed quite good until the end of the constant speed phase. Then there is a deviation.
	%(plot:limiter) Here the reason for the deviation can be seen: The output of the controller (%(variable:PI.y)) is in its limits. The anti-windup compensation works reasonably, since the input to the limiter (%(variable:PI.limiter.u)) is forced back to its limit after a transient phase.
	")}));

Creating as Draft to indicate that library officer(s) probably want/should improve them before merging.