Bugfixes

Corrections to BigInt subtraction and addition. Addition and subtraction
both tested and working correctly.
Changes to BigInt

Removed accessor function for BASE - BASE is no longer a member of the
class.
Removed QuoRem private class - object no longer used in addition and
subtraction as a result of increased efficiency.
Simplified overloaded constructors with arguments of integer types with
the addition of the convertInt function.
Reintroducing QuoRem for use in mult
BigInt mult completed

Slow multiplication (analogous to multiplication as done by hand) tested
and functioning proplerly.
mult no longer uses QuoRem.

QuoRem repurposed for div/mod results as they are computed
simultaneously with slow division (analogous to long division).