Feature Request: Verbose Command Output

[Bushuo]

While working on #102, I found it helpful to see the output of bsc. I think it would be a great addition to have a command line flag in Rewatch that allows users to view the output of the underlying commands, something like:

rewatch build --verbose

I'd be happy to submit a PR for this if you're open to it.

[rolandpeelen]

@Bushuo - A PR would be super welcome here. I've done some work here to move to env:logger but my time is slipping away from me. Perhaps you can take that as a starting point and implement @cknitt 's comment to instantiate the logger from an argument rather than from env?