Added documentation (with formulas!) to chainable.h
Added documentation (with formulas!) to chainable.h

amunmt/marian,marian-nmt/marian-train,DianaDespa/marian-train,emjotde/amunn,DianaDespa/marian-train,marian-nmt/marian-train,emjotde/amunn,afaji/Marian,emjotde/Marian,marian-nmt/marian-train,DianaDespa/marian-train,emjotde/amunn,amunmt/marian,afaji/Marian,emjotde/amunmt,marian-nmt/marian-train,emjotde/amunmt,emjotde/amunmt,DianaDespa/marian-train,amunmt/marian,afaji/Marian,emjotde/amunn,emjotde/amunmt,marian-nmt/marian-train,DianaDespa/marian-train,emjotde/Marian,afaji/Marian