Add semeval 2020 task 11
@SBrandeis : Thanks for the feedback! Just updated to use context manager for the `open`s and removed the placeholder text from the `README`! Great, thanks @ZacharySBrown !
Failing tests seem to be unrelated to your changes, merging the current master branch into yours should fix them.

Adding in propaganda detection task (task 11) from Sem Eval 2020