New release (btopipilnu-qcdf)

I have tagged the btopipilnu-qcdf release of EOS, which was used to produce the numerical results in EOS-2016-04. Noteworthy on the physics side are

• Adding one-to-two-body form factors, with the B → π π form factors being their first implementation.
• Adding the four-body decay B → π π ℓ ν to the list of available decays, both for new observables (e.g. B->pipilnu::BR) and one new signal PDF (B->pipilnu::d^3Gamma@QCDF).

On the usability side, the new Python interface allows to produce publication-quality plots. One such plot has been published in EOS-2016-04, and shows contours of the pionic forward-backward asymmetry in B → π π ℓ ν decays. The Python script that was used to produce this plot has been made available as an example.