[API BREAK] Use a nonce-generation function instead of a nonce
Implement SHA256 / HMAC-SHA256 / RFC6979.
Use rfc6979 as default nonce generation function
Merge pull request #163

bbd5ba7 Use rfc6979 as default nonce generation function (Pieter Wuille)
b37fbc2 Implement SHA256 / HMAC-SHA256 / RFC6979. (Pieter Wuille)
c6e7f4e [API BREAK] Use a nonce-generation function instead of a nonce (Pieter Wuille)