Add face detection&tracking demo
Add references to MIT+CMU frontal faces test set
Add convetor to json and truth.json
Add download script for face images
Move cmu_to_json.go outside of third_party, since it's my own code.
Move webcam demo under demos
Add cascade for frontal faces from ccv and a converter util
Move one-time utils to utils/
Merge pull request #8 from krasin/detect

Add MIT+CMU frontal face test set
Merge pull request #6 from krasin/webcam3

Add face detection&tracking demo