Pypaperbot

Added --skip-words option to specify a list of words that articles title should not contain.
Articles containing any of this words will be ignored

- added option to set DOIs as filename
- added annas archive SciDB as download source
- general improvements

Fix requirements

- Added Selenium option on scholar search to avoid bot detection
- Added --cites option to search on scholar by cites

Bug fix, closes 45

Bug fix, closes 44