:sig
String sha256(String data)

:params
data : bytes to hash
return value : the raw 32-byte SHA-256 digest

:content
Returns the SHA-256 digest of `data` as raw bytes. Prefer `sha256_hex()` when you need printable text; use the raw form when feeding the digest into other binary operations.

:example
print(sha256("abc").length(), " raw bytes, hex = ", sha256_hex("abc"), "\n");

:see
>sys
sha256_hex
hmac_sha256
