Optimize space2depth function by reducing operations number
Optimize space2depth function by reducing operations number

wkentaro/chainer,wkentaro/chainer,keisuke-umezawa/chainer,wkentaro/chainer,niboshi/chainer,ronekko/chainer,niboshi/chainer,tkerola/chainer,keisuke-umezawa/chainer,wkentaro/chainer,chainer/chainer,chainer/chainer,okuta/chainer,hvy/chainer,hvy/chainer,keisuke-umezawa/chainer,jnishi/chainer,okuta/chainer,ktnyt/chainer,chainer/chainer,jnishi/chainer,keisuke-umezawa/chainer,okuta/chainer,jnishi/chainer,niboshi/chainer,chainer/chainer,ktnyt/chainer,niboshi/chainer,rezoo/chainer,hvy/chainer,hvy/chainer,pfnet/chainer,ktnyt/chainer,anaruse/chainer,ktnyt/chainer,okuta/chainer,jnishi/chainer