Added a whole nn class containing encoder & decoder
Added a whole nn class containing encoder & decoder

Peilun-Li/dynet,dhgarrette/cnn,yoavg/cnn,Abasyoni/dynet,kamigaito/cnn,Abasyoni/dynet,mitchellstern/dynet,dhgarrette/cnn,dhgarrette/cnn,Peilun-Li/dynet,kamigaito/cnn,cherryc/dynet,Abasyoni/dynet,cherryc/dynet,yoavg/cnn,cherryc/dynet,mitchellstern/dynet,Peilun-Li/dynet