ccan: import ccan/json_out and ccan/json_escape.

These are generalized from our internal implementations.

The main difference is that 'struct json_escaped' is now 'struct
json_escape', so we replace that immediately.

The difference between lightningd's json-writing ringbuffer and the
more generic ccan/json_out is that the latter has a better API and
handles escaping transparently if something slips through (though
it does offer direct accessors so you can mess things up yourself!).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

cli/test/Makefile

@@ -12,7 +12,6 @@ CLI_TEST_COMMON_OBJS :=				\
 	common/daemon_conn.o			\
 	common/htlc_state.o			\
 	common/json.o				\
-	common/json_escaped.o			\
 	common/pseudorand.o			\
 	common/memleak.o			\
 	common/msg_queue.o			\