Init release

• Initial release
• Basic functionality:
  • Cognitex.sign_up/3 - Registers the user in the specified user pool and creates a user name, password, and user attributes defined in AWS Cognito service.
  • Cognitex.confirm_sign_up/2 - Confirms registration of a user.
  • Cognitex.admin_initiate_auth/2 - Authenticates registered user with credentials.
  • Cognitex.get_user/1 - Gets the user attributes and metadata for a user by access token.
  • Cognitex.admin_get_user/1 - Gets the specified user by username in a user pool as an administrator. Works on any user.
  • Cognitex.change_password/3 - Changes the password for a specified user in a user pool.
  • Cognitex.update_user_attributes/2 - Allows a user to update a specific attribute.
  • Cognitex.forgot_password/1 - Calling this API causes a message to be sent to the end user with a confirmation code that is required to change the user's password.
  • Cognitex.confirm_forgot_password/3 - Allows a user to enter a confirmation code to reset a forgotten password.