Implement .all() method.

[xEricL]

Please implement a aiocache.Cache.all() method to get a list of all the key:value pairs in the cache.

It would be nice if we could also filter it, such as with aiocache.Cache.all(namespace='users') to retrieve a list of all key:value pairs where the keys start with users:

[padraic-shafer]

I'm not very familiar with memcached, but a quick google search suggests that there is not a standard / reliable way to request all keys for that backend.

• SO discussion: get all keys set in memcached
• PHP implementation: Memcached::getAllKeys()

It looks like it would be straightforward for the redis backend: https://redis.io/commands/keys/

For the simple memory cache, a simple workaround in the meantime is...

cache_keys = [key for key in cache._cache if cache.startswith(namespace)]

[xEricL]

So how would I get all keys for a Redis Cache? Forgive me, I'm still new to using aiocache.