Consider opening the API

[xrstf]

I'm trying to work around issue #23. For this, I tried to simply use a custom storage implementation that has my patch (LOCK_SH) in it.

Unfortunately, nearly everything inside the Session middleware is private, so for making a simple patch to lock() I have to copy nearly everything. Not just because most of the stuff is private, but because most methods directly access the properties (instead of using a getter).

This makes it extremely hard and ugly to subclass AiP. I would suggest using protected more often and/or introducing some getters where properties must be private.