Powerspectrum estimator add threshold

[elavallee]

Please review my change to add a threshold to the PowerSpectrum estimator. The optional threshold is named: $\delta$. I updated the docstring, and I was able to pass all the tests locally. However, I did not add any new tests, which is more challenging. For an example of how to use the new feature, please see the code below.
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using DynamicalSystems, ComplexityMeasures

N1, N2, a = 101, 100001, 10

for N in (N1, N2)
    println("N: $(N)")
    t = LinRange(0, 2*a*π, N)
    x = sin.(t) # periodic
    y = sin.(t .+ cos.(t/0.5)) # periodic, complex spectrum
    z = sin.(rand(1:15, N) ./ rand(1:10, N)) # random
    w, t = trajectory(Systems.lorenz(), N÷10; Δt = 0.1, Ttr = 100) # chaotic
    w    = w[:, 1]

    for q in (x, y, z, w)
        p, ~ = probabilities_and_outcomes(PowerSpectrum(100.0), q)
        h = entropy(p)
        println("entropy: $(h).")
    end
end

[Datseris]

some simplifying and performance comments

[Datseris]

Thanks for the PR @elavallee , in addition please increment the minor version (middle number) at Project.toml file by 1 and add an entry about this change in the CHANGELOG.md file!

[elavallee]

Hi @Datseris, I appreciate your changes. I've incorporated them. I also updated the minor version number and the CHANGELOG.,md. Thank you.

[Datseris]

I'm sorry @elavallee , I forgot something in my review. There are no tests for this new feature... Can we please add a test? For example testing that the probabilities for the signal x = cos.(range(0, 2π; length = 10000) .+ 1e-2 .* randn(10000) with some δ = 0.1 are all 0 except from a single probability?

This functionality should be tested. Even though I have no doubt the code is correct as it is, it helps for forwards maintainance if all parts of the code are test covered.