SRU

Training RNNs as fast as CNNs，SRU implementatiom by tensorflow 1.4.1

I just implemented the sru code, it can run, but i have not optimizated the speed. when comparing SRU and GRU on tensorflow, SRU was not better than GRU.

refences:

[1] can run

[2] offical implementation

[3] has cuda implementation

[4] just implementation

[5] just implementation

[6] just implementation