Alkey

Also invalidate single relations: when an instance is invalidated, we
also look for any relations that the instance "belongs to" and we
invalidate their cache as well.

For example, given somethinf like:

class Order(...):
user_id = ...
user = relation(...)

Previously when saving a new order like this:

order = Order()
user.orders.append(order)

This would bust the user cache -- because sqlalchemy knew that the user
had been edited and would include it in the session's `dirty` map. However
if you saved an order like this:

order = Order(user_id=1234)

Sqlalchemy didn't pick up on the user relation. So, this release introduces
an *attempt* to pick up on these changes manually.

(At the time of writing, it's been tested successfully in a proprietary app
but the tests haven't been ported here).

Refactor the redis integration out to `pyramid_redis` and lose the `trace` module.

* wrap calls to redis with a resilient function that retries on a connection
error and fails silently when its safe to do so

* rebuild sdist without logging

* provide a reified `request.redis` client, instead of calling `request.redis()`
to get a redis client.

* add optional ``alkey.trace.trace_redis`` function to integrate the redis
client with new relic monitoring.