Rename _get_section->_get_redditor_listing.

This method is only used to return redditor listings. If
reddit adds a non-subreddit listing, then this function
might also be usable for that. However, there is a no way
to know when or if reddit will implement such a feature
nor whether this function might certainly work with it.

The benefits of this name therefore doesn't outweigh the
readability disadvantages by having a function with a name
that make it sound far more general than it actually is.
Add history scope.
Add arguments save and send_replies to submit.
Add get_new_subreddits.
Add 5 new arguments to set_settings.

These are prev_submit_text_id, submit_text, spam_comments,
spam_links and spam_selfposts.