DuckDuckGo Search improvements: past year date filter, dark theme refinements, and more

While we've been busily improving our privacy protection ducklings - like DuckDuckGo Privacy Browser (for iOS/Android) and DuckDuckGo Privacy Essentials (for Firefox/Chrome) - we haven't been neglecting our first born - DuckDuckGo Private Search! In fact, quite the opposite - we've made several improvements recently that we're excited to share with you. They should make your searching not only more effective, but also a more pleasant experience, and still of course with our same strict commitment to privacy: no personal information is associated with your searches, such that you have no search history and therefore no search profiling or ads following you around based on your searches. Some solid improvements all around, but nothing earth-shattering.