nput operation added

nput takes four parameters: number_of_iterations, size_of_key,
size_of_value and exact_size_flag.
Size_of_key is used for string/byte key types only. Exact_size_flag
[0|1] us used for generating random string of random size up to
size_of_key or size_of_value. If set to one, keys and values are of the
exact size stated.