n3fit merge-ready PR

Created by: scarlehoff

As requested during today's meeting. This PR supersedes #461 containing all the new code from n3fit in the form of 3 very elegant commits.

Note: the documentation won't compile automatically (because obv this is not merged with doc_folders) but it should work by just adding the following line to the makefile

 sphinx-apidoc -o ./source/modules/n3fit ../../n3fit/n3fit

(writing it here mainly for my own convenience)

The how to for n3fit can still be read in the text of PR #461.

If this PR works there will be a conda package in the server called n3pdf. If it doesn't work... then I'll be sad because the PR won't be so elegant anymore!

In the next PRs...

There are several things that are added in this PR because they work but I don't think they are production-ready, this corresponds to Statistics.py and the hyperopt routines.

So after this one is merged there will be two more PR:

Statistics

For a lack of a better name. This will break what is now in the Statistics module into several different files. Probably something along the lines of: stopping, animations, positivity checks.

Hyperopt

The hyperoptimization capabilities work perfectly fine, but the analysis routines are a bit of a mess since they were written as part of the analysis and were constantly changing. Now that we have a final version a lot of refactoring is needed to have them in some nice form.

Tests

Some nice 1/2-minutes long regression test would be nice to know when things change (although not sure we would want to take a difference in a fit regression tests as a failure)