Signed-off-by: XinYao1994 <xyao@cs.hku.hk>

1. add transmitter, client_choose, aggregation interface to Lib.
2. add example of how to use new added interface.

Signed-off-by: Jie Pu <pujie2@huawei.com>
Signed-off-by: XinYao1994 <xyao@cs.hku.hk>

update