feat/add review_card function

[joshdavham]

I added a new function review_card to the FSRS class to make reviewing cards more straightforward.

Now instead of having to review cards like:

rating = Rating.Good
scheduling_cards = f.repeat(card)

card = scheduling_cards[rating].card
review_log = scheduling_cards[rating].review_log

Developers can write:

rating = Rating.Good

card, review_log = f.review_card(card, rating)

Let me know if this level of abstraction is welcome 👍

Other changes:

• Bumped version from 2.3.0 -> 2.4.0
• Added test to for the review_card function
• Updated the Quickstart section in the README to use review_card

[joshdavham]

Ah that makes sense. Just like how anki shows the intervals above the review buttons.