Improve docstring of CTC
Improve docstring of CTC

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