Fix document to make a link to stack function
Fix document to make a link to stack function

keisuke-umezawa/chainer,chainer/chainer,jnishi/chainer,chainer/chainer,kashif/chainer,wkentaro/chainer,wkentaro/chainer,ktnyt/chainer,okuta/chainer,jnishi/chainer,hvy/chainer,hvy/chainer,rezoo/chainer,cupy/cupy,pfnet/chainer,kiyukuta/chainer,jnishi/chainer,chainer/chainer,ktnyt/chainer,ysekky/chainer,aonotas/chainer,wkentaro/chainer,cupy/cupy,niboshi/chainer,keisuke-umezawa/chainer,tkerola/chainer,niboshi/chainer,anaruse/chainer,niboshi/chainer,chainer/chainer,ktnyt/chainer,hvy/chainer,cupy/cupy,cupy/cupy,niboshi/chainer,ronekko/chainer,keisuke-umezawa/chainer,ktnyt/chainer,okuta/chainer,wkentaro/chainer,keisuke-umezawa/chainer,okuta/chainer,delta2323/chainer,jnishi/chainer,hvy/chainer,okuta/chainer