Merge pull request #8727 from Superjomn/doc/v2_overview2

v2 API overview refactor doc

Author: luotao1

doc/api/overview.rst

@@ -7,10 +7,6 @@ it proposes some high-level concepts such as `Layers <http://www.paddlepaddle.or
 A model is composed of the computation described by a group of `Layers`, with `Evaluator` to define the error, `Optimizer` to update the parameters and `Data Reader` to feed in the data.
 
 We also provide the `interface for Training and Inference <http://www.paddlepaddle.org/docs/develop/api/en/v2/run_logic.html>`_ to help control the training and inference phrase,
-it has several easy to use methods
+it has several easy to use methods to better expose the internal running details, different `events <http://www.paddlepaddle.org/docs/develop/api/en/v2/run_logic.html#event>`_ are available to users by writing some callbacks.
 
-- `paddle.train` 
-- `paddle.test`
-- `paddle.infer`
-
-to better expose the internal running details, different `events <http://www.paddlepaddle.org/docs/develop/api/en/v2/run_logic.html#event>`_ are available to users by writing some callbacks.
+All in all, the V2 API gives a higher abstraction and make PaddlePaddle programs require fiew lines of code.