Moments parameterization

[aimalz]

@elts6570 found an implementation of approximating a PDF from its moments.

[elts6570]

@aimalz The code is called pymaxent and can be downloaded here: https://github.com/saadgroup/PyMaxEnt. It has no pip package, so I downloaded src/pymaxent.py locally.

[aimalz]

Just to sync this with the discussion in LSSTDESC/bayesian-pipelines-cosmology#5, this is probably not the best option for this parameterization.

Update: PyMaxEnt might be okay after all, pending some modification of the default way of obtaining moments illustrated here.

[aimalz]

A good sprint day activity would be to tackle this issue, since @elts6570 has implemented a successful PDF reconstruction in a notebook here.

[aimalz]

This issue subsumes #96, so I'm closing that one but referencing it here so the discussion is still accessible.