emoji_eventsLRU cache

Build LRUCache(capacity), a cache that forgets the least recently used key when it is full.

• get(key) returns the value, or None when the key is missing. Reading a key makes it the most recently used.
• put(key, value) stores the value (updating counts as use). When the cache is over capacity, drop the least recently used key.
• Both operations should be O(1).

Acceptance criteria

• Don't use functools.lru_cache.
• The tests at the bottom print All tests passed.

Hint: collections.OrderedDict has move_to_end() and popitem(last=False).