Code review comment for lp:~leonardr/lazr.restful/basic-auth

As discussed in IRC:

1. please rename "check_credentials" to "authenticate_user"
2. ensure the check_credentials docstring is valid ReST, i.e. add an indent on the second line of :return:.
3. please document either the __init__ parameters or the ivars
4. please rename BasicAuthMiddleware.regex to something more intuitive like secure_path_pattern.