Add squared_difference to __init__
Add squared_difference to __init__

keisuke-umezawa/chainer,chainer/chainer,chainer/chainer,tkerola/chainer,keisuke-umezawa/chainer,hvy/chainer,niboshi/chainer,keisuke-umezawa/chainer,okuta/chainer,okuta/chainer,niboshi/chainer,keisuke-umezawa/chainer,chainer/chainer,wkentaro/chainer,hvy/chainer,chainer/chainer,wkentaro/chainer,okuta/chainer,hvy/chainer,hvy/chainer,pfnet/chainer,niboshi/chainer,wkentaro/chainer,niboshi/chainer,wkentaro/chainer,okuta/chainer