implement some coherence-based dual-mic noise reduction algorithm

refer to

• [1] N. Yousefian and P. C. Loizou, "A Dual-Microphone Speech Enhancement Algorithm Based on the Coherence Function," in IEEE Transactions on Audio, Speech, and Language Processing, vol. 20, no. 2, pp. 599-609, Feb. 2012.

• [2] N. Yousefian and P. C. Loizou, “A dual-microphone　algorithm　that can cope with competing-talker scenarios,” IEEE Trans. Audio, Speech,Lng. Process., vol. 21, no. 1, pp. 145–155, 2013.

• [3] Yousefian, N., Hansen, J. H. L., & Loizou, P. C. (2015). A Hybrid Coherence Model for Noise Reduction in Reverberant Environments. IEEE Signal Processing Letters, 22(3), 279–282. doi:10.1109/lsp.2014.2352352 

• [4] Ji, Y., Byun, J., Park, Y. (2017) Coherence-Based Dual-Channel Noise Reduction Algorithm in a Complex Noisy Environment. Proc. Interspeech 2017