Add the implementation of TCP Store

[sandyhouse]

PR types

New features

PR changes

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Describe

Add the implementation of TCP Store (kv-database) for communication.

usage：

import datetime
import paddle


store = paddle.fluid.core.TCPStore(
                     "127.0.0.1",  # master address
                     6170,           # master port
                     True,            # is master
                     1,                  # world_size
                     datetime.timedelta(0) # timeout
               )
        store.add("my", 3)
        ret1 = store.get('my')
        store.add("my", 3)
        ret2 = store.get('my')
        assert ret1[0] + 3 == ret2[0]

TODO:

1. add the timeout for store operations

[paddle-bot-old]

Thanks for your contribution!
Please wait for the result of CI firstly. See Paddle CI Manual for details.

[gongweibao]

store = paddle.fluid.core.TCPStore这个路径是不是太长？

[sandyhouse]

store = paddle.fluid.core.TCPStore这个路径是不是太长？

这个是pybind暴露路径，后面会import到paddle.distributed.TCPstore(python端路径）

[ForFishes]

LGTM