Phoenix 1.3 JWT Auth API with Guardian JWTs, password hashing

@script @Voger Just published the React Native section of this tutorial in two parts (split the React Native section into two): https://medium.com/@njwest/building-a-react-native-jwt-client-efacf78b9364

Will likely make some tweaks here and there, but please have a look and let me know what you think! :slight_smile: