Created the WCSMutableFraction class.
Redeclared the properties to make them readwrite, and then synthesized them.
Declared all of the new methods for WCSMutableFraction.
Changed _DNU_numerator and denominator to _AOII_
Imported WCSFraction.h and started the definitions of the new methods.
Defined the setNumerator and denominator method.
Defined modifyByAdding method.
Finished defining the last new methods.