launch spider in new thread

I had a problem where I could not stop the spider with ctrl+c. As a solution it is now possible to launch the spider in a new thread.
In settings set 'threaded' to True and spider.start() becomes non-blocking. Since Pholcidae now inherits from [threading.Thread](https://docs.python.org/2/library/threading.html#thread-objects) you can use all those methods (.isAlive(), .join(),..) on it aswell. If you want to stop the crawl from outside the spider-thread, simple call spider.stop().
I have updated test.py to reflect this.
Also, 'threaded' defaults to False. Which means that if threading is not explicitly activated it is not used and behaves exactly the same as now (backward compatible)

added option to launch spider in new thread;
added start/stop functionality;
added __init__.py;
updated test.py;
PEP8 (flake8) compliant