Change RSS default importer to accomodate multiple values in <dc:creator>

Problem/Motivation

Standard RSS feed can include multiple tags, for example, PubMed Feed

Currently only one is imported.

Steps to reproduce

Create new RSS feed, add text field to a content type and map import from Author Name.

You can see that only first value is imported. It might be useful to import all authors in a predefined format. Proposed format would be comma separated, for example,
Markus Eyting
Min Xie
Felix Michalik

will generate Markus Eyting, Min Xie, Felix Michalik

Proposed resolution

Add option to import "All Authors" to default configuration for RSS feed