fix(password): Update the flag comparison

[ciphersaw]

The example CheckPassword("Aa12345", N|L_OR_U, 6) returned false before, but it returns true with the latest flag comparison logic.

The details of update is shown as following:

1. Update the comments in password/password.go
2. Update the test examples in password/password_test.go
3. Update the flag comparison logic:
   • L_OR_U: It should include either the lowercase or the uppercase letter.
   • L_OR_U|L: It must include the lowercase letter, while the uppercase letter is optional.
   • L_OR_U|U: It must include the uppercase letter, while the lowercase letter is optional.
   • L_OR_U|L|U: It must include both the lowercase and the uppercase letter, which is equal to L|U.