* update Conv2D_cn.rst, test=develop

* update conv and pool op, test=develop

* fix Conv2DTranspose_cn.rst, Conv2D_cn.rst, test=develop

* add comment for class Layer, test=develop

* add comment for class Layer, test=develop

* add comment for dygraph layer, test=develop

* add comment for dygraph layer, test=develop

* add comment for name, test=develop