is_authenticated and friends are methods, not properties

`is_authenticated()` and friends are properties, not methods. The
documentation mistakenly referred to them as properties. If you used
them in a conditional as if they were properties, they would always
evaluate to `True`.
Merge pull request #175 from lpsinger/anonymous_user_methods

is_authenticated and friends are methods, not properties
Support Unicode for user-ids in Cookies

The payload is unicode anyway.
str(...) will break if the user-id is unicode.
Add test case for unicode user_id in cookies

This test cases fail with 0.3.0 of flask-login.
Handling unicode user_id's worked except for storing in cookies in the past.
is_authenticated and friends as properties

The documentation mistakenly referred to is_authenticated and friends as
properties, when in reality they were methods. However, they make good
sense as properties. This patch turns them into properties.