* add docstring of three eager method

* test=docs_preview

* update element size bind

* update docs of numpy, clone, clear_gradient, element_size; test=docs_preview

* refine clear_gradient docs; test=docs_preview

* refine element_size docs; test=docs_preview

* add detach doc; test=docs_preview

* empty commit; test=docs_preview

* update signature; test=docs_preview

* refactor; test=docs_preview

* empty commit; test=docs_preview

* add docstring of Tensor

* empty commit; test=docs_preview

* refine TensorDoc; test=docs_preview

* refine TensorDoc; test=docs_preview

* remove extra indent in TensorDoc; test=docs_preview

* remove a space; test=docs_preview

* move docs ahead of implementation; test=docs_preview

* refine

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Co-authored-by: Nwj-Mcat <1435130236@qq.com>
Co-authored-by: NSigureMo <sigure.qaq@gmail.com>