Strip out :qlc from LRW implementation

[whitfin]

This fixes #329. Rather than fix the issue with :qlc, I figured it might just be best to avoid it directly.

Instead we now use Cachex.stream/2 for the LRW policy, which under the hood now uses :ets.select/3 thanks to #352. This means the implementation is now much easier to understand, and is just built on top of other Cachex structures. I'm not sure if there's a performance hit, my benchmarking was inconclusive (although there's a chance it's faster, even?).

I also took the opportunity to rename Cachex.Query.create/2 to Cachex.Query.where/2 as this now reads a bit better (even if it could still be improved):

# what does this mean?
Cachex.Query.create(true)

# "where true" implies "all"
Cachex.Query.where(true)