A class used to represent multiprecision integers that makes efficient use
of allocated space by allowing a number to occupy only part of an array so
that the arrays do not have to be reallocated as often. When performing an
operation with many iterations the array used to hold a number is only
reallocated when necessary and does not have to be the same size as the
number it represents. A mutable number allows calculations to occur on the
same number without having to create a new number for every step of the
calculation as it occurs with NUMBERs.