They're generally used pass-by-copy (unusual for C structs, but
convenient they're basically u64) and all possibly problematic
operations return WARN_UNUSED_RESULT bool to make you handle the
over/underflow cases.
The new #include in json.h means we bolt11.c sees the amount.h definition
of MSAT_PER_BTC, so delete its local version.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Rusty Russell