Enhanced enum support

[MichalLytek]

Right now, you support string array as an enum:

// Enum-like type and definition example.
type Gender = 'male' | 'female';
const Genders = {
  MALE: 'male' as Gender,
  FEMALE: 'female' as Gender,
};

@prop({ enum: Object.values(Genders) })
gender?: Gender;

However we have string enum support in TS now. It would be nice if the decorator function accept also the object type as the enum value and get the string values using Object.values(object) inside:

// true enum type
enum Gender {
  MALE = 'male',
  FEMALE = 'female',
};

@prop({ enum: Gender })
gender?: Gender;

So the signature of the BasePropOptions would be enum?: string[]|object; and you can in runtime check if Array.isArray(enum) to behave like now or convert enum object to values.

[MichalLytek]

I can make a PR if you want 😉

[szokodiakos]

Hello! Yes, when I saw the new string enums I wanted to make this but currently don't have enough time for it. A PR would be awesome indeed!