flavio v0.6.0

In this new release, branching ratios and angular observables of the decays B_s->phi l l have been added. The implementation takes into account the sizable width difference between the two B_s mass eigenstates. The observables correspond to the time-averaged ones measured at hadron colliders like the LHC.

The B_s->phi form factors are based on arXiv:1503.05534, the mixing formalism on arXiv:1502.05509. Thanks to Javier Virto for discussions and cross-checks!