No `get_din` method implemented

[michaelosthege]

There is a set method (related issue #4) but no get method.

I'll try to do a PR, possibly alongside refactoring the implementations like @cpr-bar and I discussed recently.

[cpr-bar]

This is intentional because the DINs' states are sent with high frequency in the state message and thus a member of CRIController.robot_state: RobotState.

[michaelosthege]

Ah got it, thanks!

I would still consider a get_dio method to make it more discoverable.