Split authors returned from Kindle

[ahobsonsayers]

If a book has multiple authors, there are all returned as one string. We should split this strong and return the authors as an array.

An example of this is "Good and Valuable Consideration" by Lee Child and Joseph Finder

[ahobsonsayers]

Audiobookshelf does not support retrieving anything but as single author as a string from custom metadata providers. Before we do this, the Audiobookshelf will need to support custom metadata providers that return multiple authors as an array.