Support optional dtype in creations
Support optional dtype in creations

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