Config-file lines consist of a keyword and data.  The keyword, which is
case-insensitive, consists of everything from the first non-whitespace
character to the next whitespace character, or the end of line if there
is no following whitespace character.  If there are no non-whitespace
characters at all, or if the first such is a #, the line is a comment
and is ignored.

The data begins with the first non-whitespace character after the
keyword.  (This implies it cannot begin with whitespace.)

If a file ends with a partial line (ie, it has a last character but it
isn't a newline), a newline is supplied.  Note that this means that a
partial line ending a file read with @ does not merge with the line
after the @ - to put it another way, @ operates at a level where files
are streams of lines, not streams of bytes.

@ FILE
	FILE is read and its contents effectively inserted in place of
	this line.

key KEY
	The cloud key is literally KEY.

keyfile KEYFILE
	KEYFILE is read and the contents are the cloud key.  If the
	file is larger than 64K, only the first 64K is used.

	Note that no transformations are applied to the file's
	contents; for example, using "key foo" is not the same as doing
	"echo foo > foofile" and then using "keyfile foofile", because
	the file will contain a fourth character, a newline, and a
	three-character key "foo" is as different from a four-character
	key "foo\n" as any other two distinct keys are.

id N
	This member's cloud ID is N; N must be in 0..255.

ip ADDR
	ADDR is one of this member's cloud IPs.  This may be given
	multiple times; the resulting addresses accumulate.

type T
	This member's type is T.  T can be (case-insensitive)

		public	This cloud member is type 1 or 2; it pays
			attention to PUBLIC packets and tries to
			maintain connections to the endpoints in them.

		private	This cloud member is type 3 or 4; it ignores
			PUBLIC packets, using only the address(es) it
			has been configured with by `uplink' lines.

listen ADDR/PORT [TYPE]
	This host is type 1 (or 4) and should listen on ADDR/PORT for
	cloud connections.  This may be given multiple times to listen
	on multiple endpoints.  The special strings *, *4, and *6 may
	be given for ADDR to listen on all local addresses, all local
	IPv4 addresses, and all local IPv6 addresses, respectively.

	TYPE is optional and may be "public" or "private".  Public
	listening points are advertised in PUBLIC packets; private ones
	aren't.  If TYPE is not given, listening points at RFC-1918
	private addresses (for IPv4) or link-local or site-local
	addresses (for IPV6) are private and others are public.

uplink ADDR/PORT
	This can be given multiple times, and the contact points
	accumulate.  For a type 1 or 2 host, these give initial entry
	points into the public cloud; for types 3 and 4, these list the
	host's uplink(s).  Uplinks configured this way never expire, in
	contrast to uplinks learned from PUBLIC messages.

tun N [TYPE]
tun DEVPATH [TYPE]
	These specify the tun device.  If the argument is a number
	(anything accepted by strtol(3) with third argument 0), the
	device pathname is constructed from it a la /dev/tun%d;
	otherwise, the argument is used directly.  (To use an
	all-numeric name as the device node, prefix it with a path,
	using ./ if necessary.)

	The optional TYPE may be POINTOPOINT or BROADCAST
	(case-insensitive).  If specified, the tun interface mode is
	changed (with TUNSIFMODE) to that value.  If neither is
	specified, no attempt to change the interface type is made.

	There is no escaping mechanism; it is not possible to use a
	DEVPATH string containing whitespace.