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>
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