Add ability to filter out articles with keywords from the feed.

[JohnnyNoArms]

First, I want to say that I just installed Raven Reader and it looks really good. I'm using this for something specific - I'm probably an edge case - and I get a lot of "articles" in my feed. There are quite a few articles that I definitely don't ever need to see and they have certain words in their titles. I would love if I could filter out those articles by blacklisting keywords.