Add mapping for enumeration and option values

[taquitos]

Right now enums and options are transcoded as whatever primitive values they are backed by. It would be nice to be able to provide strings that map to those values:
typedef NS_ENUM(NSInteger, MyEnum) {
MyEnumAValue = 1,
MyEnumSecondValue,
MyEnumThirdValue
};
so MyEnumSecondValue could map to "SecondValue" in the JSON instead of "2" (and so on)

[taquitos]

option bit masks would be interesting....