Update controller.py

[Bernicorn]

implemented the IDM longitudinal controller

[eleurent]

Hello Bernicorn,

I do not understand the purpose of this PR, since the IDM longitudinal controller is already implemented in https://github.com/eleurent/highway-env/blob/3ef36a0fb17f91769ecac9581206bd51cce41108/highway_env/vehicle/behavior.py#L12 which is a subclass of ControlledVehicle.

[Bernicorn]

First of all i´m a beginner in python and programming. That was my first try to do this^^
Still three months ago, we talked about it in issue #133 and you asked about it to make a pull request. I´ve added the feature, that the controller is deactivated during the lanechange. Thats why i made this new function.
If the controller is activated during a lanechange, the controller protect the agent from an crash. If the agent will do any critical decisions, like an dangerous lanechange, he will get no penalty for it.

[eleurent]

Right, okay.
However, your proposed change results in duplicated code, which is not ideal.
I think that a better solution would be to propose a new ActionType, which uses the existing IDMVehicle behavioral model for the ego-vehicle, and executes lateral actions.

I'll propose an updated version