Loading known articles into a set

Using a set for constant-time accesses.
Adding a new Database object

I’ll try to use this object to manage the database instead of the more
procedural approach I’d been using before.

Also, starting a test for this object.
Adding method to load known articles

Article md5sums are loaded into a set, which is then saved as an object
attribute.
Adding a few assertions
New implementation of add_article
Methods to check if article is in db
Refactor of test classes and a few more tests
Renaming the article_in_db method
Using the Database object now
Test for has_article()
Printing the number of new articles
Removing deprecated methods
Adding a natcap query python file

Contains natcap query information, specifically.