Update README.md

Add performance test example.

zhongkaifu#1. Adding bias cell for LSTM

Merge branch 'master' of https://github.com/zhongkaifu/RNNSharp.git

Update README.md

zhongkaifu#1. Fix RNNSharp crashing bug when dense feature isn't used

zhongkaifu#2. Improve BiRNN learning process
zhongkaifu#3. Support to train model without validated corpus

Refactoring BiRNN