flav-io/flavio v1.1

The first minor release in the v1.x series brings a couple of new observables and some other improvements. Many of these improvements where motivated by smelli and special thanks go to Jason Aebischer, Jacky Kumar, and Peter Stangl.

• More leptonic LFV τ decays: τ→3e, τ^-→e^-μ⁺μ^-, τ^-→e^-μ⁺e^-, τ^-→μ^-e⁺μ^-
• τ→πl and τ→Kl (implemented by @jackypheno)
• K_S→πlν

• Improved treatment of likelihoods of τ LFV limits
• Implemented the B form factors from a combined fit to an improved LCSR calculation and LQCD results in arXiv:1811.00983. These form factors have been made the default for B→π and B→K.
• Updated all particle masses and widths to PDG 2018 values
• Other parameter updates: f_K and f_π from FLAG; B bag parameters now use the FLAG average for the SM operator
• Consistent treatment of scale dependence of longitudinal meson decay constants (implemented by @peterstangl)

• A missing factor of 2 in the dipole contribution to τ→3l was fixed (thanks to Andrzej Buras [yes!] for noticing this)