For users who didn't specify a cookieName, I think they would be annoyed to find that in a major upgrade they had to either
A) Refactor their code from `req.session` to `req.session_state`
B) Add a `cookieName` set to `session` which would cause a loss of session upon deployment.

How do you feel about...

The session will be placed in the request object a property that is the same name as the cookieName. For backwards compatibility, the first use of this middleware when the `requestKey` option is not specified and the cookieName is not `session`, then the default value will be `session`.

OR

Do you have a better name than `requestKey`? Breaking backwards compatibility without a win is kind of a bummer.