Add authentication documentation for Blerg::Database
=head1 MODULE FUNCTIONS
+=head2 GENERAL
+
=over
=item exists(name)
=back
+=head2 AUTHENTICATION
+
+=over
+
+=item auth_set_password(username, password)
+
+Sets the password for the given username. Returns 1 on success, 0 otherwise.
+
+=item auth_check_password(username, password)
+
+Checks the password for the given username. Returns 1 on successful
+authentication, 0 on failed authentication or error.
+
+=item auth_login(username, password)
+
+Authenticates and logs the user in. Returns the authentication token if
+successful, or undef on failure or error.
+
+=item auth_logout(username, token)
+
+Logs the given user out if the token represents a valid session. Returns 1 on
+success, or 0 on failure. Failure can happen if the token is no longer valid
+(meaning the user has been automatically logged out), so the return status is
+probably best ignored..
+
+=item auth_check_token(username, token)
+
+Checks that the token represents a valid session for the given username.
+Returns 1 if the session is valid, 0 otherwise. Also resets the expiration
+time of the session.
+
+=back
+
=head1 CONSTRUCTOR
=over