"BigFraction(double)" is unnecessary

Constructor BigFraction(double value) is only called from the from(double value) method.
Actually, this constructor is misleading as it is indeed primarily a conversion from which appropriate numerator and denominator fields are computed; those could be set by
the "direct" constructor BigFraction(BigInteger num, BigInteger den).

Moreover, the private field ZERO goes through this conversion code whereas it could constructed "directly", e.g. using of(0). Similarly for field ONE.