crypto/shachain/tools: update to new rbuf API. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
shachain: allow overriding of number of bits, add cmdline tool. lightning uses 48 bits, so this provides a quick utility for our test vectors, and provides a nice example. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>