Adds Anthony Liu's Study with 2048 to variants.yml

This variant of mine enables users to study with 2048. It spawns question "?" tiles that, when merged, presents the user with a question. The game is paused until they answer it. Players can copy and paste the link to any Quizlet flashcard set (Quizlet.com is a popular website that allows people to create online flashcards). In this way, Study with 2048 can be used to study for any kind of test or exam, since Quizlet has a huge library of flashcards. This variant also makes it really easy to change the frequency of the question blocks, from 0% to 33% of all tiles.