## Fixes#111
> The modulo operator on this calculator gives the result that is different to the most used calculators.
The current `modrate` function is the equivalent of rem(...)/remainder(...), not mod(...)/modulo(...) available in some popular Math apps.
### Description of the changes:
- rename `modrate` in `remrate` to be more accurate.
- add `modrate`, calculating modulo similarly to Matlab, Bing, Google calculator, Maxima, Wolfram Alpha and Microsoft Excel
- Add `RationalMath::Mod` using `modrate` as an alternative to `Rational::operator%` using `remrate`
- Add a helper `SIGN` to retrieve the sign of a `Rational`.
- modify `CalcEngine` to use `modrate` in Normal and Scientific mode and `remrate` in Programmer mode.
### How changes were validated:
- manually and unit tests added
* Convert Rational::Negate to an operator override
* Convert Rational::Add to + and += operator overrides.
* Convert Rational::Sub to - and -= operator overrides.
* Convert Rational::Div and ::Mul to use /, /=, *, *= operator overrides.
* Convert Rational::Mod to use %= and % operator overrides
* Convert Rational::Rsh and ::Lsh to use >>=, >>, <<=, << operator overrides
* Convert Rational::And, ::Or, ::Xor to use &=, &, |=, |, ^=, ^ operator overrides
* Convert Rational relational functions to operator overrides
* Remove unnecessary precision arguments from Rational class and remove use of explicit Rational constructors in favor of implicit conversions for value types
* Remove unnecessary precision variable from RationalMath operations
* Replace unnecessary Rational::Not with Xor operation
* Remove unnecessary Rational::IsZero() in favor of == 0 comparisons
* Fix rounding issues in ratpak that result from using large precisions.
* Move assignment stmt out of IsCurrentTooBigForTrig
- Separates values from the representation (base/radix) of those values.
- Uses a single base for all values represented as Rationals.
- Rationals are converted to/from a specific base when they are converted to/from strings.
* Converts NumObj* functions to use Rationals. Places new functions under CalcEngine::RationalMath namespace
* Moves functions that correspond to an operator to the Rational class with intent to convert to operators in the future
* Consolidates use of RatPack's NUMBER and RAT data types to Number/Rational classes and RationalMath namespace.
