doc: Add additional special methods in class template
doc: Add additional special methods in class template

Mainly used in:
- Datasetes
- Iterators
- Variable and Parameter

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