New observables: Higgs production and decay, beta decays, e<sup>+</sup>e<sup>-</sup> scattering, kaon and pion decays
This release adds a large number of new observables that have been recently implemented in [flavio 2.0](https://github.com/flav-io/flavio/releases/tag/v2.0.0) (based on [arXiv:1911.07866](https://arxiv.org/abs/1911.07866) by Adam Falkowski and David Straub and a collaboration of Martín Gonzalez-Alonso, Adam Falkowski, and David Straub):
- 32 new observables in the likelihood `fast_likelihood_quarks.yaml`: kaon decays, pion decays, nuclear and neutron beta decays,
- 48 observables in the new likelihood `likelihood_eeww.yaml`: total and differential cross sections of e<sup>+</sup>e<sup>-</sup>→W<sup>+</sup>W<sup>-</sup>,
- 33 observables in the new likelihood `likelihood_higgs.yaml`: Higgs signal strengths.
This raises the total number of observables taken into account in the global likelihood to 399.
New feature
The CKM scheme used by a `GlobalLikelihood` instance can now be selected on instantiation using the optional argument `ckm_scheme`. This will facilitate the use of different CKM schemes in the future (currently, only one default CKM scheme is defined).
Bugs fixed
- Removed the branching ratio of Λ<sub>b</sub>→Λμμ in the [1.1, 6] GeV<sup>2</sup> bin.
- If a `GlobalLikelihood` instance is created with the argument `fix_ckm=True`, now the default CKM elements from flavio are used instead of those defined by the default CKM scheme.
Other updates
The required flavio version is now [v2.0](https://github.com/flav-io/flavio/releases/tag/v2.0.0). The flavio version is not pinned anymore to allow updating flavio from pip before updating smelli.