some feature request

[liuliqiang]

i'm so happy to find out your good project --redisco and i try this lib in my personal project however i think it can be better if it has more feature such as:

1. add options in fields, so we can define the field like this: status = Attribute(required=True, options=['draft', 'private', 'publish', 'trash']
2. add Reference List Field, such we can has a reference field list like: categories = ListField(ReferenceField('Category'))
3. i found that all index field in redis was saves index as a set, whether can we save it as a string if we set this field unique=True

that's all my suggestion, i hope it can help improve redisco...thx..

[stuaxo]

For #1 it looks like you want a feature like djangos ChoiceField.

#2 looks like a variation on #1 (especially if options could accept a callable).

Different storage strategies seems like it could be interesting, though I guess it complicates the implementation slightly, maybe you would be up for doing an example implementation for one of the field types ?