allow any collection to be marked as read

[koriroys]

My goal is to mark a collection of books as read. I don't want to mark all as read, just a select subset.

I'm attempting to use unread like so:

books = current_user.expensive_books # just some custom query that is a subset of books
Book.mark_as_read!(books, for: current_user)

It breaks with the current code as books isn't type Array. I can turn the query into an array I suppose, but I'd rather just pass the collection itself in as is. Does that seem reasonable?

[coveralls]

Coverage remained the same at 100.0% when pulling 8b207d0 on koriroys:kjr/collection-fix into 4cfe8ec on ledermann:master.

[ledermann]

Great, thanks!

[koriroys]

Probably should update the name of mark_array_as_read at to reflect this as well.