flav-io/flavio: v2.0: Higgs, beta decays, EDMs, charm, and a new maintainer

This release is a significant milestone for the flavio project. First, it contains a huge number of new observables, justifying the major version bump. Second, the baton of maintaining the project is passed from @DavidMStraub to @peterstangl from this release on. After extending from flavour physics to electroweak precision tests in v1.0 and subsequently adding EDMs and many other "unflavoured" precision observables, this release brings flavio several huge steps closer to becoming a universal observable calculator for all observables where new physics contributions can be described in the framework of the SMEFT. The list of observables has been updated in the documentation. Concentrating on flavio's role as an observable calculator and likelihood generator, we also removed some old and poorly maintained submodules, notably statistics.fits. Here's everything that's new: Higgs physics Based on arXiv:1911.07866 by Adam Falkowski and David Straub, this release contains everything that is needed for an up-to-date analysis of Higgs physics at LHC - predictions and measurements (Run 1 & Run 2) of the signal strengths in all channels! Nuclear and neutron beta decays Based on a collaboration of Martín Gonzalez-Alonso, Adam Falkowski, and David Straub, this release contains Ft values of doubly allowed nuclear beta decays necessary for EFT analyses of new physics in d→u transitions. In addition, also the neutron lifetime and all relevant correlation coefficients in neutron beta decay are included! Atomic and molecular EDMs Electric dipole moments of paramagnetic atoms and molecules have been added, based on arXiv:1809.09114. Semi-leptonic D decays The decays D→(π, K)lν including all relevant measurements (even binned differential distributions). New B→D and *B→D** form factors The form factors have been updated to use the results from arXiv:1908.09398. Unit tests against EOS added with the help of @dvandyk. Utilities for units and elements The new flavio.physics.units module can come in handy for converting between units. Look at the source to see what it provides. The new flavio.physics.elements module provides two functions to convert between element symbols (e.g. Ag) and the atomic number Z (e.g. 47): symbol(Z) and Z(symbol). Other improvements flavio now supports Python 3.8 Some parameters and measurements updated Breaking changes The flavio.statistics.fits and flavio.statistics.fitters modules have been removed as we are concentrating on the main features of flavio as observable calculator and likelihood generator. These modules had been poorly maintained in the recent past. Code using the fits module can be ported fairly simply to the more recent (and more powerful) flavio.statistics.likelihood module