WIP: Add rllib agent and rollout script

Make repository a package

This will enable the rllib stuff to run correctly, remove some weird path hacking, and is generally a better development strategy

We batch rollout evaluations, like in the standard rollout script.

Currently needs a docker container with at least 2.5 Gb RAM, otherwise it crashes.

An example of a successful submission (of an admittedly very bad agent) can be seen here: https://gitlab.aicrowd.com/robert_kirk/neurips-2021-nethack-challenge/-/issues/12