Would like to get some feedback on usability/API in addition to the underlying issue.

The main trade-off I see is between keeping the API generic/raw versus making it more specialized.

The current approach is quite generic in that it provides a mechanism to return an io.Writer. However, this means that consumers need to create loggers themselves, and also need to provide the path to the logger files themselves (var/log/service.log, etc.).

Another possible approach would be to have a function that returns a set of loggers (service1log, metric1log, etc.). This would remove the need for callers constructing their own loggers and providing path to output. However, this makes the API a bit more fragile (if any of the logger types change in the future, the function would need to change), and for things like the service logger we would need to take extra parameters to specify things like the logger level. We would also want to make it clear that the returned logger doesn't update by default, and that if that behavior is desired the client would need to implement it.

Let me know if you guys have thoughts on this.

I've put up an alternate implementation at #99. I think I may prefer that alternate approach as one that has better balance/trade-offs, but open to feedback.