Moved exact existing intelligibility enhancement implementation into new repository for reference when making further changes. Note: this cl does not add these files to any gyp. Original cl is at https://webrtc-codereview.appspot.com/52719004/ . TBR=aluebs@webrtc.org Review URL: https://codereview.webrtc.org/1177953006. Cr-Commit-Position: refs/heads/master@{#9441}