Support to split object properties to separate columns.

[liudonghua123]

Say If I have the following classes for serialization to csv.

@dataclass
class Link:
    title: str
    url: str
    
@dataclass
class SearchResult:	
    paper_name: Link
    authors: list[Link]
    publication: Link

I want to split paper_name into paper_name.title and paper_name.url columns in the generated csv file.

See also #33 (comment).

Maybe some annotation can be used on the classes of the property type to indicate the purpose.