[Feature request] Hash key support

[rdong8]

I'm looking for an equivalent to a feature like this from the cachetools library. For instance, an app could use multiple DB connections to fetch the same data, even though those connections might not have the same image under the hash. Without the ability to exclude the DB connection from the hash key, you'd incur unnecessary cache misses.

[Dreamsorcerer]

I think this library is meant to be a simple replacement for lru_cache. So if it's not something in lru_cache, then we probably won't end up supporting it here.