(get-membership-old): Use a "want-read-texts : BOOL" argument instead

	of "mask : BITSTRING(want-read-texts)".  The result is the
	same, but using BOOL makes the prototype easier to read.
	Document the argument more verbosely.
(get-membership): Do likewise.
(login): Do likewise for the "invisible" argument.
(create-anonymous-text-old): Added @misc{} markup.