Create periodogram for Epoch folding

[matteobachetti]

Created here in HENDRICS for convenience, with the basic information that should be available at the very least:
https://github.com/StingraySoftware/HENDRICS/blob/master/hendrics/io.py#L62

[swapsha96]

@matteobachetti @abigailStev I would like to work on this. I wanted to know all the requirements for this? Do I need to create all the function that are in hendrics/io.py?

[matteobachetti]

@swapsha96 no, it is just a periodogram like Powerspectrum that contains frequencies and EF statistics. io.py contains a lot of functions that are not needed in Stingray.

[Gaurav17Joshi]

@matteobachetti, I am working on this problem, I have created a class Pulsar_Periodogram that takes in an Event list and a frequency array, calculates the $EF$ and $Z_2$ Statistics for the same. It also plots the periodograms, using its functions.

Also I wanted to ask that fold_detection_level and z2_n_detection_level , are missing from pulse.pulsar, have they been removed? I think, they have to be used to get the peaks and fit gaussian and sinc curves to the periodogram.