This makes for more useful errors. It prints where it was up to in
the guide, but doesn't print the entire JSON it's scanning.
Suggested-by: Christian Decker
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
In several places we want to access the first element of an array.
This uses a '[indexnum:xxx]' form which is a bit weird, but works similarly
to the way we specify member matches.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This takes a JSON-style format string, and does intelligent parsing,
removing a lot of boilerplate from code which needs to deal with JSON.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
