deno task should separate parallel task output

[dsherret]

Something we never got around to in the initial implementation.

[NfNitLoop]

I'd love this! I'm debugging some very odd race conditions in my task dependencies and it's not always straightforward to know where errors are coming from.

Another thing that would help making sense of parallel task execution:

• (Optionally?) Include timestamps for when tasks start/stop execution.

That way I can ensure that my dependencies are running in the desired order. (I'm starting to wonder if that's the case w/ my debugging! And you can't rely on the order of things on stdout, before or after this change, to know what order things ran in, or whether they had overlapping execution times.)