Improve return field selection and serialization

[tylerhutcherson]

Right now in order to deserialize an embedding field, you need to call:

qry.return_field("embedding", decode_field=False)
qry.return_fields("title","year")

which is less ideally from a UX perspective. This feature was added as a simple wrapper around the redis-py classes. But we can try to simplify this ux for sure.