[Request] Allow to init BigInt with signum and byte array

[iTanChi]

Like the JVM BigInteger, it would be greate to support this constructor. JVM doc:

    /**
     * Translates the sign-magnitude representation of a BigInteger into a
     * BigInteger.  The sign is represented as an integer signum value: -1 for
     * negative, 0 for zero, or 1 for positive.  The magnitude is a byte array
     * in <i>big-endian</i> byte-order: the most significant byte is the
     * zeroth element.  A zero-length magnitude array is permissible, and will
     * result in a BigInteger value of 0, whether signum is -1, 0 or 1.  The
     * {@code magnitude} array is assumed to be unchanged for the duration of
     * the constructor call.
     *
     * @param  signum signum of the number (-1 for negative, 0 for zero, 1
     *         for positive).
     * @param  magnitude big-endian binary representation of the magnitude of
     *         the number.
     * @throws NumberFormatException {@code signum} is not one of the three
     *         legal values (-1, 0, and 1), or {@code signum} is 0 and
     *         {@code magnitude} contains one or more non-zero bytes.
     */
    public BigInteger(int signum, byte[] magnitude) {
         this(signum, magnitude, 0, magnitude.length);
    }

[soywiz]

What's your use-case for this? What's the difference between +-bigInt.absoluteValue?

[iTanChi]

@soywiz When doing some crypto things, I usually do with byte array and convert it to BigInt. I can do by converting byte array to hex and then hex to BigInt but it's not so convenient, also, I see that the lib has been storing the data and signum already