Add tests

[pwnfoo]

TSSIA

[Double-A-92]

For unit tests to make sense you first have to refactor the code into smaller units.
Especially the _do_ocr_and_lookup funcion is way too big and handles 3-4 responsibilities, when it could actually be split very nicely.

E.g. do_ocr would be a nice testable unit. Input an image and get username and text back, no need to worry about the twitter api or anything else in that function.

Other functions woud be get_user_tweets, compare_ocr_with_tweet_list, print_results, ...

Maybe I'll give it a try tomorrow... :)