Add methods to estimate_delay

[Datseris]

In particular, you can do:

• First zero of correlation function
• First minimum of correlation function
• Exponential decay of correlation function (currently implemented)
• minimum of the mutual information [1]

Also, maybe it is time to move estimate delay and dimension to DynamicalSystemsBase.jl ?

[1] : A.M. Fraser, H.L Swinney, Independent coordinates for strange attractors from mutual information, Phys. Rev. A 33 (1986) 1134--1140.

[Datseris]

Connected with #12

[Datseris]

We now have all of the above methods. BUT: the method using the mutual information needs work.

Specifically, we are following from this PR: https://github.com/JuliaDynamics/DynamicalSystemsBase.jl/pull/42 made by @halleysfifthinc.

I am commenting here what still needs to be done:

• [ ] tests!!! For both mutual_info and estimate_delay with the mutual_info method.
• [ ] docstring in mutual_info, including the paper where it was taken from
• [ ] Add the mutual_info method to the docstring of estimate_delay.

The following are optional:

• [ ] See whether performance gains can be made.
• [ ] Answer: Does the method work with Euclidean distance as well? It gives a speedup of 4x.

@halleysfifthinc I am tagging you here to be aware of the changes. If you want to finish this "PR" (which now is simply an issue), feel free to assign yourself here.