This patch adds new hashing alhorythm bcrypt_sha256, which is based on
the bcrypt but does not have limitations on the leght of the passwords,
since passwords are passed through HMAC-SHA2-256 first.
At accepts exactly same parameters as bcrypt does.
However, it prefix the hash using `prefix` attribute rather then
`indent_values` which are same as for bcrypt.
Change-Id: I5430ebf5a20142c1a9caab960ced9b3ee2e782c1