[Rivet] 2 new CMS plugins

[Janssen Xavier]

Hi,

FYI, I just pushed 2 plugins to the contrib directory:
CMS_2016_I1413748: Measurements of ttbar spin correlations and top quark polarization using dilepton final states in pp collisions at sqrt(s) = 8 TeV
CMS_2016_I1430892: Measurements of ttbar charge asymmetry using dilepton final states in pp collisions at sqrt(s) = 8 TeV

Cheers, Xavier.