Idea for DeviceManagerIO, ScreenIO, KeyboardIO

[tomhea]

Inspired from rereading #154.
The idea is simple. The input/output will be connected to DeviceManagerIO, which is a device that handles multiple IO devices.
An idea: for controlling N devices (including the DeviceManager), you output 1 and then ceil(log2(N)) bits to indicate to which device you want to talk, or 0 to keep talking to the same device.
Then you can talk to each device.