Support passing byte_array into crypto functions

[Pieter12345]

This adds a way to perform the existing crypto functions using both byte_array keys and values. I needed this for signing a HTTP request to access an AWS S3 bucket, which works with this modification.

Note that I also needed the following code to convert the returned hex string to a byte array:

proc _hex_to_ba(string @hex) {
	byte_array @ret = byte_array();
	for(int @i = 0, @i < length(@hex), @i += 2) {
		int @val = parse_int(substr(@hex, @i, @i + 2), 16);
		ba_put_byte(@ret, if(@val < 128, @val, @val - 256));
	}
	return(@ret);
}

It could be helpful to add some hex_string_to_ba() function to provide this functionality out of the box, or add some option to make the hmac functions return a byte array instead of a hex string. If this is the case, issues should be created for those feature requests.