Add a simplify function to fraction type

[pirsonxyz]

This is useful when dealing with big fractions that can be simplified

[dnsl48]

Hi @pirsonxyz, all fractions are simplified by default in the constructor, unless you are using GenericFraction::new_raw method, which primary discrepancy is the lack of simplification for performance reasons. Thus, you could use the GenericFraction::new constructor as the way to simplify a fraction.