Add support for Sessions

[rabbiveesh]

After some research, the issue that I wanted to address in #10 really was something else.

Apparently, in order to get release health, you need support for sessions, as per the docs here. It seems like that's usually set up via an option auto_session_tracking.

It would make sense to treat a req/res cycle as a "session", and automatically wrap that as documented there.

[pmb0]

Hi, I'll get it done, but I can't say exactly when yet.

PRs welcome. :)