Config-file lines consist of a keyword and data.  The keyword 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.

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

		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
	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.

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).