Adds DeferredList to twisted crawler's fetch_urls function
Adds url to return value

*removes errbacks
Adds twist_grab fn
Fixes bug that shuts down program after reactor stops

* replaces react function with a reactor
* restructures return value of callback so times can be gotten from there
Removes excess whitespace
Adds classes for consuming and producing links from the crawl
Adds README for twisted crawler specifically
Implements Crawler class and producer/consumer libraries (separate from one another)
Adds API methods
Updates example
Restructures producer class to accept a destination
Adds update_frontier method
First testable Version

* bug: even with certain lines commented out (see code), the reactor keeps running
Replaces the main function with one without the top layer of abstraction (crawler)
Adds item to to-do list
Adds items to .gitignore