API changes
   * The output parameter of mbedtls_sha512_finish_ret, mbedtls_sha512_ret,
     mbedtls_sha256_finish_ret and mbedtls_sha256_ret now has a pointer type
     rather than array type. This removes spurious warnings in some compilers
     when outputting a SHA-384 or SHA-224 hash into a buffer of exactly
     the hash size.