updates configs for scraper job
moves 'runner' scripts into exmaples folder
moves paging logic from Listings.extract back into 'runner' script

This commit breaks the 'separation of concerns' principle in that the
extraction step from ETL is split across two methods instead of
encapsulated in the class method.

This is best approach given the constraints of:
(1) avoiding paging through ALL craigslistings of section X just to
    find the new listings for X;
(2) keeping the global logic sane and readable: we're just scraping
    craigslist FFS.
documents new structure and design