improve output to educate user about what is happening

use color. state what task is being executed. then show commands for a task execution. then state time of execution. for example, in the `serial/workflow.yaml` (which consists of two tasks), it should look something like this:

```
<green>data/reuters21578</green>
mkdir -p data/reuters21578
tar xzf data/reuters21578.tar.gz -C data/reuters21578
                                                                    0.12 s
```