Output streams

[g105b]

When a command outputs something, it needs to be grouped into its own output stream.

Each stream can be provided a different colour, after #4 is implemented. For non-coloured terminals, the name of the command that is being output can be shown along with a timestamp before the message.

For example, two long-running processes "time" and "status" that make output every few seconds:

[time] 2020-04-05 17:25:53
The time is twenty five minutes past five.

[status] 2020-04-05 17:25:59
OK

[time] 2020-04-05 17:26:03
The time is twenty six minutes past five.

[status]  2020-04-05 17:26:10
OK